that happened to me for a while as well i think you just need to catch her at a certain time. i was able to get through to her.
No, it's not that...she goes offline when she doesn't want to take a chat, stays off for a bit then comes back on. It's happened more than 5 times for me (I just did it to test, I don't want to even read with her tbh lol) and EVERY time it's the same thing. She did the same to my friend last year.
Maybe sometimes she chooses to block, and others just ignore the person until they give up, who knows.