M.R.
Does she see a Developmental Pediatrician? I am not positive, mine have seen one for later developmental issues, but it seems to me that she needs to have a doctor that will oversee all the interventions and check into something that the therapists do not see on a regular basis. Maybe a pediatric neurologist?
Hypertonia is a frequent issue for kids with a myriad of developmental issues, but it sounds like she is doing very well and you are well poised to access all the early intervention she may need.
I would be asking each of the questions you raised to a doctor who can help, those are my hunches, but ask your pediatrician for a referal!
Mine are hypotonic- and have the weak core strenth, is there some combination of the two?
M.