My initial advice would have been to keep the Motability car, but its not practical, if you want your daughter to still drive. Returning the car ASAP, so you aren’t throwing money away on something thats not practicable.
The next best route, I guess would to buy a used car for her, as leasing may pose insurance problems and may not be adapted to your daughters needs.
There are a couple of possible ways of getting adaptions, depending on her requirements:
1: New from adaptions installer (no VAT)
2: Used or ex demo from adaptions installer, though you may not get what you want.
3: Ebay is worth a look, as there are always a good selection of used adaptions available, as well as some new and ex demo. Depending on the adaption, the cheapest way to install is by youeself or family member or local mechanic / adaptions installer, if they are prepared to do so.
4: No harm asking Motability if you or adaptions installer can take the adaptions of the car prior to returning. This maybe possible without asking, but I’m not the one to ask on that.