What Causes Lack Of Balance Long After A Brain Injury?

My sister has traumatic brain injury sustained when she was 39. She is 63 now and basically in good health--heart, lungs, etc. Her worst problem is her lack of. Balance. Lately this has worsened to the point that it s impossible to get her to use her walker. She wants to be in wheelchair constantly. I think her overall coordination has worsened, too. She got off Methodone some months ago with good effects. Her substitute for keeping severe leg pain to a minimum was to have Lyrica prescribed--450 mg per day, I believe. I am wondering if this medication is worsening her balance and coordination. What do you think?