Hi H.,
My first question is does she have an ear infection? Not all babies get fussy with them but the movement of turning over and laying there could be throwing her equilibrium off, making her dizzy and uncomfortable so she doesn't want to turn back over. Two of my kids have had ear infections that we never new about until we went into the doctor for something else. No crying, no ear pulling, no fever, absolutely nothing.
I don't want to be an alarmist, but after six kids I do have a little experience especially since my kids are all special needs (they are adopted) so I have had to learn a lot about child development. By 8.5 months, she should be easily rolling herself both ways. If she's not able to, then you need to talk with her pediatrician even if she's meeting her other milestones. My one daughter struggled terribly to turn over even after she was walking, so if she is still making her other milestones it doesn't necessarily mean everything is okay. My daughter had issues that had to be addressed by early intervention services. Now at almost 5 y.o. she can do age appropriate stuff, but if really watch the way she moves you can tell she uses her muscles differently than other children.
First of all, don't panic from what I said. I do have questions though because if you do want to take her to the doc over this then maybe I can help with some other things the doc may need to know that a lot of people wouldn't realize are red flags. Is she sitting? Is she self-feeding? Does she seem to not like certain movements, textures, or sounds? Does she cry easily or avoid certain situations? Does she have reflux or allergies?
You can e-mail me if you want and you think the situation warrants it. I hope I didn't scare you because that was not my intention.
L.