I don't know why noone else has replied, but suicide is one thing you should ask her directly about.
This is a situation I've been in myself, several times. I usually follow a process of working from the very unspecific, down to very specific questions, to ease people into talking about what they may never have articulated to anyone else.
I might say to her, that I'd been thinking about the conversation we'd had, and I thought I might have misinterpreted what she said. And then I'd ask her directly, whether when she'd said she didn't want to be here, did she mean her house, a particular place, or in general.
If she says some particular place, that's your cue to act enlightened, and ask if you can help that happen in some way - you would have offered earlier if you'd not been so dim.
If she says "in general", then ask her directly if she means she wants to die?
Then you can ask if she just generally wants to die, or if she's thought about actually killing herself?
Has she thought about how to do it?
Does she have a plan? You don't need to know what it is.
Does she have a date or time?
Is that date or time soon, or far away?
The further you get down this line of questioning, the more worried you should be. Just generically "not wanting to be here" is really quite normal (at least in my social circles - I'm autistic, and so are my friends, so generally other people would really we weren't here as well
), thinking seriously about ways and means to make sure you aren't is not.
If she has a plan, and/or time, tell her that you don't mind talking about it, that you're genuinely interested. Tell her that it's common, but that it's usually a sign of illness, like a high temperature.
Ask if she's in contact with any professionals about it. Who are they? Possibilities range from GP, counsellor, to CMHT and crisis team. Don't expect them to be very helpful, mental health budgets are minimal.
If not, ask if she'd like help getting in touch with some. Offer it. Go with her if she'd like. Disregard what I said above - some professionals are absolute stars, and she might be lucky.
Ask her to let you know if her plans change. If you're happy to be rung up at 3am just to listen to someone cry down the phone at you, let her know.
Make plans with her to do things, if she's up for them.
Above all, don't promise things you can't deliver on