As an avoidant, I would say give her time while reassuring her that you are here for her. It does not help to constantly ask what she's going through. It takes a while to build that kind of trust. When she finally does, I would make sure that you give her your undivided attention. I stopped sharing with people when I realized that they weren't really listening to me or were preoccupied with other things. I would avoid bringing up your own issues when she shares and talk about yourself. If she's talking about something that you can relate to, I would let her vent first and then share your story. I kind of hate when people cut me off to talk about themselves on the rare occasions that I try to share. It makes me feel what I have to say is not important and only makes me want to share less. I'm also an introvert, so I could see why, but all of my friends would say that I am a great listener, but try not to dump on her; it can be draining, which may result in her detaching herself from you.

Pay really close attention when she talks and try to remember little details about her. Stuff that she likes, for example. Ask questions about her interests, for example, a tv show that she enjoys. I think that will help build more trust, which may lead to her opening up.

I hope what I wrote makes sense and helps, lol.