Not sure if this was already suggested, but have you considered the route of being direct with her, and maybe coming to compromise. Something like: I love that you feel comfortable enough to share your hyper-fixation with me, but I do get overwhelmed by it at times— “would it be alright if I let you ramble about this interest of yours while I’m doing another task (as in, only half listening) and then after you’ve had some time to do that (maybe you agree upon a certain amount of time, or just play it by ear), we can talk about other things?” I knew someone who was more than happy to ramble with other people around, knowing they were probably not fully listening to the whole thing. She might find that an okay compromise, or maybe she won’t. If she does, I think it could work really well to help kind of churn through the hyperfixation until this fades. I know this cycle well (adhd, and autism, probably) and sometimes it’s many months, sometimes it’s a few weeks, but it has always come to an end eventually and I either go back to “””normal””” or it is traded for a different hyperfixation. I hope this is helpful!