She takes her shoes back once they're well away from shore. Are there any other boats nearby?

There's somebody fishing over there and a yacht farther off.

Then she should keep rowing until they're very far away. (Rowing is very unpleasant, and she can't even have an Unseen Servant do it, but it is very motivating to remember she will DIE and DISSOLVE FOREVER if she makes the slightest mistake.)

Eventually she can be in an unoccupied area of sea, all the boats mere dots where she certainly couldn't tell if they were going to dump anyone overboard.

Okay.

She takes her coat back from Asmodia too. 

The backpack is full of pitons for mountain climbing. It's heavy. She puts it on Asmodia. She ties it in the front with rope, across Asmodia's chest and across her waist. She - 

- it's surprisingly hard? Maybe she should've requested more shifts on the front lines at the Worldwound, so she wouldn't be squeamish. 

She decides to use the cantrip Jolt first, and the knife only once Asmodia is dead. There'll be less blood that way but that's not why she's doing it. 

She hits Asmodia with a little itty bitty lightning bolt. It usually doesn't kill people, even civilians, unless you get unlucky, but she can do it as many times as needed.

Asmodia twitches all over and winds up kicking Carissa in the leg. She holds position when she stops, in a ridiculous spasmodic pose maintained in perfect stillness.

She's really not a person. It is still murder but this is because Pharasma and local law are both stupid. She is not - dissolving - something that wants to not dissolve.

She does another lightning bolt.

She goes limp, this time.

And another two, just in case.

Asmodia doesn't react. Sure is handy she doesn't scream, the other boats might have been able to hear something.

If she were capable of screaming this wouldn't be necessary!

She takes the knife and does her best to make Asmodia totally unrecognizable. As far as she can determine there's no chance she'll float until enough things have rotted for the tied-on backpack to slide off her, and by then she shouldn't be recognizable anyway, but if she gets this wrong she will DIE and DISSOLVE FOREVER so she had better be sure.

Now there's a lot of blood.

She dumps Asmodia over the side of the boat and then cleans it off very systematically with Prestidigitation. She needs to get every inch of the boat and her clothes. - also she nicks her own finger with the knife and bandages it with a scrap of cloth so if she did miss a spot she can explain it, but she should still be extraordinarily careful not to. 

Then she sets off for Flute Island.

The island has a... hill. It's tall enough that you could float off the top but that means it's forty feet vertically from shore to peak. But it has interesting surfaces to climb up and some people are climbing up it, and there's a little village on the beachy end of the island, with a couple restaurants and a store and an inn.

She ties up her boat and takes the extra pair of shoes and goes looking for Asmodia.

Asmodia is near but not in the village, in an area with some trees where casual observers won't run into her, but not too hard to find if you're expecting her. "Still nothing," she says, troubled.

"I'm sorry. And you don't think I - mismade you -"

"If you made a mistake that ought to affect my suitability as a cleric it wasn't an obvious one. - I've learned that most people can't make two people in a row, one right after another," she adds. "I overheard it mentioned on the ferry."

" - huh. The books all chided you to not - go into it thinking you'd just make another if this one turned out wrong - but they didn't specifically say it was impossible - do you know how long you ordinarily have to wait?"

"I think it's less than a year based on context but I don't know by how much."

Nod. "Well. Let's head back. - I think you should pretend to wake up tomorrow or the day after, so that it's not connected with the boat trip."

"I don't think I can perfectly emulate her. I can try - walking more normally and looking around a little but not speaking, and you can say you wondered if a change of scenery would help, or something."

"Sounds good."

And she rows them back. Asks Asmodia to check if she can see any blood spots anywhere Carissa missed.

Asmodia finds a bit in her hair.

Note to self, wear a hat while committing murders. 

She drops Asmodia off at the shore somewhere mostly deserted, returns the rental, goes over to the shore to get her.