I don't think either of you are being unreasonable in this situation.
This is proper armchair psychology stuff but I wonder whether you feel hurt by this because as a child, you weren't able to voice what was happening to you, or to seek help. Or if you did try, no one listened. Now as an adult, you don't (I hope) need rescuing from an abusive environment, and you are old enough to have that voice, but someone you trust is still not willing to listen, so it brings back those feelings of not being seen.
From your friend's position, she doesn't see someone who needs to be rescued or 'heard' - she feels that in you she has found someone whose company she enjoys and with whom she can relax and have fun. When confronted with sad and traumatising stories about your childhood, that feeling of having fun and relaxing with a friend is extinguished like a light, and she starts feeling all the negative feelings any of us feel when reading a tragic story in the news. But unlike with news stories, she can't just switch it off, or say 'this is depressing, let's talk about something else'. That would be very rude and unfeeling. So when you offered her an out, she took it.
As PP have said, you are perhaps looking for different things from this friendship. So perhaps you need to just let it fade. Or alternatively you could take what she is offering and find someone more suitable to explore your trauma with.
For the record, I personally have to switch off from a lot of sad stuff because if I don't, it sends me into a spiral of depression and anxiety, or an existential crisis. For me this is usually stories about people being diagnosed with or dying from an incurable disease young - I immediately start feeling like it's going to happen to me or someone in my family. So I hide stories like this in my news feeds. This may seem selfish and uncaring, but it's just what I have to do to stop myself from wallowing in fear and despair. I also sometimes find myself unable to stop thinking about, for example, recent tragic news stories involving children being abused/murdered, and can end up sobbing my heart out. I have to remind myself not to borrow grief from others.
I'm so sorry for what you have been through. You deserve to be heard and I wish you luck as you continue on that journey.