Then, she will not notice at all, when a portalsnake appears in her room and decides to eat her?

Not per se, but she definitely notices the whole being-uncotted part afterwards!  Sleep and accidental blanket self-bondage and blindfolding don't make for the least disorienting of combinations but she has other senses - where is she, what sort of place?  Is anyone around?

She is in what appears to be a brightly lit torture chamber!* There is a blue-clad torturer** who is leaning over his victim*** with sinister instruments!

*dentist's office
**dentist
***victim

What the fuck!  She yeets her sleep mask at the floor, detangles the blanket from her legs, kips up, and - runs out of the room??  If the door's locked she'll check for windows to jump out of.

The door's locked. The dentist palms open a compartment in his torture instrument caddy thing and produces a device and shoots her with it and she falls unconscious.

Then she wakes up.

What.  What.

Well where is she this time.

She is in a similar torture chamber. She looks alone. She isn't alone.

Actually, come to think of it, the dentist also wasn't alone! And there were several extra dudes in the torture instrument caddy!

But, most relevantly: she has company.

<Hiya, I'm Ispalt!>

On the one hand it does not do her credit that her immediate instinct in the previous situation was to run the fuck away, but also she could hardly have rescued anyone if she was about to get tortured herself, and she's still totally going to do the exact -

She's still going -

She's -

<Yeah, no, that's not going to work while I'm driving, hon. Work with me and we can avoid the vivisection scenario thing though!>

The what.

<See, that thing you do where you can copy stuff from other people? Isn't a thing here. Ain't nobody can do that. And if you go tell everybody as soon as I let go of you for one teensy tiny second, this is bad for me, because then I never get you back and you're very cozy, and it is bad for you, because they take you apart trying to figure it out. Capisce?>

She definitely doesn't want to get taken apart; it would probably be fine in the long-term but what if something got her throat wrong and she couldn't heal it without taking someone else's voice and then her voice would be lost forever and it's such a good voice.

Nonetheless - she can see the person in her head (ew) but can she take anything from them?  Such as ideally (this is so surreal) control of her own body??

<Nopily-dopily! If you could do that I would've yelled for the folks next door and then stunned us again so you could be taken off my metaphorical hands. I'm driving.>

Colley wishes whatever this is had happened to her her girlfriend instead.  That's not an awful thing to think because she's pretty sure her girlfriend would have preferred it too.

How does she - is it just directing thoughts at her new pal (derogatory) - <I can't copy context from you, can you please fill me in on the basics.>

<Yeah-huh,> says Ispalt, getting up off the torment chair and shaking out their hair. <I dunno where the ass you're from but this is planet Earth, where there are humans who don't do that, and I am from the Yeerk homeworld - well, I was born in space, but ancestrally speaking - where people also don't do that, and us Yeerks are here on Earth collecting hosts so we can survive having a war with the folks from the Andalite homeworld, where they sort of do that but it's dramatically more complicated and also mostly involves turning into animals wholesale and yeah it's not actually the same. I can cozy up in your brain for a few days and then I need to go for a swim. During which time standard operating procedure is that you are thoroughly locked up, of course, but usually they don't gag you, so you could still spill the beans. I'd rather you did not. You'd rather you did not. Win-win if you shut your face about having weird powers.>

. . . <Sure.>  Tentatively.

<I reckon I have a few days to win you over to the cause of Not Getting Vivisected. I mean, for one thing, you wouldn't hafta be conscious while they looked for weird glands or whatever, so no need to get the idea that you could fight them off with the strength of Whoever and the speed of Whoever Else. Now I'm gonna go lie your ass off to the boss and we will figure out what is next for me 'n you, mkay?>

She pushes open the door and leans into the next room, where a little grey-green slug is being administered to the patient* in the dental chair. She yoinks the language from the dentist, since Colley does not in point of fact have it. "Yeah, boss, she doesn't know how she got here either, I'm pretty sure she was high. Fancy outfit for a homeless vagrant, right? She can't even remember where she swiped it. I think she'll detox okay though. Can I crash in your guy's spare room till -"

"No, no way, he has neighbors, they'll talk," says the dentist, as the slug slithers into the patient's* ear. "Get cash out of the ATM and get a hotel for now. Report to the pool to get reassigned."

"You betcha, boss!"

And she lets them out of the dentist's office.

*victim

Colley si - she does not sigh, not even once they're outside and out of earshot.  Ugh.

It occurs to her that Ispalt might be able to make her into whatever kind of person they want, if they're the one controlling the copying power, which is the WORST POSSIBLE thing to have realized and she's going to concentrate very hard on composing more of her opera now.  It's annoying that she can't hum or play along or write anything down but that doesn't actually impair her in keeping track of six lines of harmony.

<I don't need to, hon, not unless you turn out to be the kind of person who is super planning to sprout knives out your arms and scream to everyone that you have exciting powers the second I go on vaycay. Though separately there isn't a rule that you've gotta be such a sweetie, if you're sick of it.>

<No thanks.>  She's gone traveling before and while it wasn't really legal to change herself in certain ways it also wouldn't have been enforced as long as she put things back before she came home.  But what's possible, that seems important to know - <You can try and make me think your body is less gross.>  It doesn't really rate next to everything else but she can see it and it's in her head and this probably only isn't nauseating because she clearly isn't responsible for her own nausea right now.

<Harsh. Unfortunately I don't super care for it either, I'd rather have yours.> Elevator.

Colley skips over forming an opinion on whether or not that was a socially appropriate opinion to have and/or express.  <What's this,> she wonders of the elevator, and to a lesser degree of everything around her that's at a higher tech level than she's used to.

<Elevator. It's going to be very annoying hiding how wacky you are while also not myself having seen most things in the world. Fortunately you have useful powers.> She grabs context from the building doorman and from three random passersby till she knows how to find an ATM and book a hotel room.

<Why haven't you?>

<You're my first host! I've like, heard stuff. But we don't super have eyes.>