She’s starting to develop an emotional dependence on you. I would hesitate before assuming romantic interest, it’s perfectly possible for girls to develop these dependencies on guys without any romantic intention at all. They likely don’t even realize they’re doing it.
This can get to be onerous if you don’t handle it carefully. You don’t want to be turned into an emotional dump for all her problems, particularly those involving guys she is romantically interested in.
If she starts to cross a line, gently stop her and tell her the conversation is getting too personal and you don’t really feel comfortable talking like this with just a friend. If she doesn’t respect your wishes and expects you to keep listening to her problems, stop taking her calls for a week or so. That will send the message, crystal clear.
If you’re romantically inclined towards her, you can ask if she would like to be your girlfriend. But you have to be really gentle here because you’re playing with forces that can ruin your friendship. If she says yes, great, if she says no, then you will need to develop really good boundaries to make sure you’re not getting walked on.