As long as they're really close together, she can manage quite a few of them. In fact, if she makes a row of candles very very close together, she can affect them all at once even when each individual candle is way out of separate-candle range of most of the rest. It seems like what might be happening is that she can only control or extinguish "one" fire at a time, but the definition of "one fire" is a little bit flexible.

Aha.

She takes notes and conjures a metal sheet on the ground for fire protection and then sees how much fire she can create and control at once.

She can fill about two cubic feet of air with flames, and reshape the blob of fire to her liking, although she's not great at fine detail yet. Any bigger than that gets abruptly much harder, and she can't pull the fire-blob apart into multiple pieces at all.

She will work on expanding total volume, then.

Her volume capacity expands slowly but steadily. She can work on her fine control at the same time if she likes, and that one seems to go a little faster.

Yes she will do that.

Does the rose also grant fire resistance? She checks.

It grants moderate fire resistance. She can still burn herself, but she has to try pretty hard.

So if she wants to make a halo out of fairly cool flame she won't set her hair on fire?

Correct! She can have her burning halo. It's very fetching.

The number limit is really annoying. Without it she could layer her petal ballgown with an ornate design of flames.

Oh well.

She takes it off her head and experiments with how hot she can make it.

There's an upper limit. It's pretty hot - definitely hotter than those candle flames. She might have difficulty measuring it without a specialized thermometer. If she works at it, she can get the limit to creep upward, but it's hard to tell how much progress she's making.

Is it hot enough to turn blue?

Yes, although there's still some orange at the edges.

Alright. She'll play around a bit with conjuring various metallic salts inside the fire and seeing how much color detail she can get that way.

So many colours! Kind of hard to get much precision out of it, but it's doable!

She'll practice with that for a while then. 

Eventually she goes looking for Anna and Cass in order to show off.

They're in their rooms, with the door ajar. Sounds like they're rehashing an age-old friendly argument about their respective taste in music. Probably safe to interrupt.

She knocks anyway.

Cass comes to get it.

"Hey, what's up?"

"Wanna see what I can do with the fire rose?"

"Definitely!"

"Me too!" says Anna, coming to the door.

She grins and conjures a ball of orange flame in the palm of her hand, shrinks it and heats it to blue, then has it "bloom" outward to form a six-petaled flower shape, with each "petal" fed a different salt by her conjuring so that they form a rainbow. Then the flower dissolves into a rainbow-striped cylinder that follows Emily's hand as she twirls, bringing it around to form a diagonal hoop around herself.The hoop splits into what appears to be several intersecting hoops that make a sort of bowtie pattern, one horizontal and the others at different diagonals, lowers her hands so that the tips of her fingers brush the lowest hoop-edges, then brings them up, the "hoops" following until they consist of an arch over her head. This she "grabs" at both ends, letting it widen and flatten into a shawl-like shape, drapes it over her shoulders, and finally lets the fire go out.

Anna applauds.

"Artist in the house," says Cass.