How do you describe vomiting ?

the main take away is that you usually start to feel the taste of your saliva changing a bit and getting somewhat warmer. then you start heaving and at this point you better run to the nearest toilet, trash can or makeshift container. once you start vomiting, it burns a lot. your throat is going to feel burned but it's like a chemical burn and a lot of the vomit can go up thru your nostrils at which point your nostrils will burn too. once you're done you feel extremely weak and tired.

Sometimes it's really easy, the stuff just rushes up your throat and out, but often it's a struggle. Honestly, if you've never vomited, don't try to describe it. Most people know how it feels, so just say "She vomited" and then go on about how she had to rinse her mouth and wipe her eyes before she felt better.

If she has long hair, she'll need to hold it out of the way while she vomits. A good friend will do that for you.

Let's assume you aren't trolling.

Here's the thing, you actually don't need to describe what she feels at the moment.

Since pretty much everybody knows how it feels you could totally wing it by remaining deliberately vague and let the readers fill out the blanks. They most likely wouldn't even notice that you didn't actually describe the feeling.

Read a couple of descriptions of other people or ask your friends. Or observe how some people react and what they do when they have to throw up.

What's more, I think most readers won't want to read three paragraphs of detailed vomit descriptions.

Upchuck or driving the porcelain bus

I've never eaten McDonalds, tell me what it tastes like.  It's impossible without referring it to something else.  There is nothing else that feels like vomiting.  Why don't you just stick your fingers down your throat and vomit.  It's not difficult and you'll have some experience.  Alternatively, don't write about things you don't know.