It's possible she's right, but IMO, three is too young to get a good diagnosis (which she's not qualified to make, in any case.) If you haven't already, start him on a really firm routine, work in lots of transitions so he's ready for them (You get three more blocks, then we put them away. . . one, two, three, okay, back into the box they go!") and generally make his world as predictable and focussed as you can. And I second the take-him-out-of-that-class suggestion; at three, there's no good reason to leave him in a class with someone who isn't dealing well with him, no matter what the reason. You may find that if he goes to a different class, he'll be a changed kid.
If you're still having these problems when he's six or seven, and if he's falling behind in school by that point (i.e. not reading somewhat independently by grade 2) then consider a more formal, medical assessment.