My (18F) best friend (18F) just confessed that she's in love with me

First time posting on Dating.mobi so bear with me :/
My (18F) best friend (also 18F) just confessed that she's in love with me. This came as no surprise. We've known each other since we were little kids and lately, she's been dropping a lot of hints that she's interested in me romantically. This summer she broke up with her boyfriend (in name only, they never went on dates and only really called each other partners at school) and has been telling me that she's been in love with a girl. It's been heavily implied that this girl is me, but I defaulted to my usual practice of ignoring the situation, pretending to be oblivious, and letting the person with a crush on me make the first move.
Well, this week she made the first move. I live pretty far away from her because we go to different schools, but she sent me a really lovely letter confessing her love. In the letter were all sorts of cute momentos and pictures and even a song playlist of romantic oldies. She's a really sweet person, is kind to absolutely everyone, and I really like the idea of being in a relationship with her. The distance wouldn't be a problem because I'm planning on transferring to a school closer to home next semester. Her letter told me to take my time responding and that she'd continue to be my best friend no matter what my response was.
It all sounds like a dream come true... except for three big problems...
1) I've had very little experience when it comes to relationships and I'm really not sure what my sexuality is. All I know for relatively sure is that I'm not interested in boys and that I had a maybe crush on a heterosexual female friend of mine who I'm no longer in contact with. The girl who just confessed to me has been my best friend for more than a decade and I don't want to hurt her or think of her as an "experiment".
2) My mental health is trash. I've been in worse slumps, but I'm seriously struggling to function in my day to day life. This is the main reason why I'm moving back closer to home. I'm confused about my feelings for my best friend is because I haven't been feeling a lot of things in general lately. Everything has just been meh. She's amazingly supportive of this, but it's not something she should have to deal with in a relationship.
3) My family is homophobic. I love them so much, and they're one of the few things that still make me happy, but we live in a very conservative area and they would not be happy if I started dating a girl. I need to be on the best terms I can be with my family because I'm moving back. I don't know how long I could hide that I'm in a relationship with my friend and I don't think it's fair to her to have to hide it.
Should I try things out with her? Since she's so supportive we could probably test things out and if it causes problems we go back to being just friends. Or should I tell her to wait until my situation gets better?
Either way, how do I respond without hurting her?
TL;DR! My (18F) childhood best friend (18 F) just confessed her feelings to me and I'd love to try and be in a relationship with her but my mental health is a dumpster fire and my family is homophobic.


Source.