My therapists assume things about me all the time and it drives me nuts.

I don’t know L, but based on what you quoted she doesn’t seem to be assuming to me. Putting quotes around “knowing” and “is” suggest to me that she’s saying in fact she doesn’t know for sure, i.e., she’s not assuming, hence the quotes. At least that’s what those quotes would mean if I used them like that. The whole sentence seems to indicate uncertainty to me, not assumption.

But maybe I’m misreading since I don’t know the context.