Hey Kate,
I will say “they” most likely mean she’s with another woman. It seems like you probably already know this, but you are looking for some confirmation. “they” and/or “person” are the big words when not wanting to lie, but at the same time, not come straight out either..
She is trying to tell you, so you should just come out and ask her. I know when I first started accepting my lifestyle, I was the same using those same terms out of fear of what the other might feel and/or think, and I just wished there was a way for them to find out without me having to be the one to say “hey, by the way, I’m gay”. It would have just made life easier if they would just ask or just blend it into our life as if it was just like anything else. It takes time for one to get to that point where you can just be so open, so you can help her by being the one to help her come out to you. She will see how much support she will be getting from you, so it just will make it that much easier for the next person she wants to come out to.
In regards to the unfortunate surrounding she is faced with in her community/ school, I suggest to for her to start with her counselor. She needs to explain her fears, and seek help from the school in finding ways with dealing with the ignorance/ lack of knowledge of our lifestyles there. Unfortunately, it might not make a difference in her time while she’s attending, but it makes them aware and perhaps will help the next generation as it is a process to make people understand and see the realization of the hatred/discrimination put upon us.
You can also have her research info on support groups for teen gays; there are plenty of websites that can direct her to find them in her community. Here’s a link to start with: http://www.saim.us/resources.html
She is lucky to have you in her life; she will need all the support she can get in dealing with this next chapter in her life. Thank you!