It sounds like your friend is going through a really tough time and is reaching out for support. Even if you're not emotionally ready to engage deeply, it's still important to acknowledge her feelings and let her know that you care. Here’s a possible response you could consider:
"Hey, I just saw your message. I’m really sorry to hear that you’re feeling this way. I can’t offer the support you need right now, but I want you to know that I care about you. Please consider talking to someone who can help you through this., whether it’s a trusted adult, a counselor, or a friend. You deserve support, and I hope you can find someone who can be there for you."
This response validates her feelings and encourages her to seek help while also being honest about your current emotional capacity.