Jessica,
I agree with what Christine has said.
My mom has had two hemiglossectomies-one in January, and then again in July. We weren't sure what to expect after the first surgery. Her flap and face were very strikingly swollen, and she could not close her mouth for at least a week and half to two weeks. All we could see was the flap, a huge incision, and very little of the "native tongue." The reconstruction surgeon explained that sometimes with thigh flaps, the flaps can be a little too big. He said better too big than too small in terms of function (the bigger the flap, the easier it is to make contact with the palate to initiate a swallow or make some speech sounds), and eventually shaving the flap down would be a comparatively easy procedure. After a month, it looked much better. She was able to close her mouth around her tongue, and was much more intelligible, but her speech was definitely affected-she sounded as if she'd had a stroke. It was getting better, though. This was without speech therapy. She had to have radiation very soon after her surgery, and the radiation also shrunk up the flap some too. I don't think it made sense for her to have speech therapy at that time since they were about to wage war on her poor oral tissues.
For the second hemiglossectomy, they had to take more tissue. The flap (from her other thigh) was smaller-I think because they had to use a portion of the graft to reconstruct tissue in her throat and on her neck. This time, they took more toward the base of tongue and throat, and she required a PEG tube. She's in speech now, but mainly for swallowing therapy. They waited to initiate therapy until she healed a bit more (about 8 weeks). It seems that it takes time, and once she heals a bit more, I'm sure your mom will benefit from some speech therapy.
I'm wishing all the best for your mom, and some peace of mind for you.