Don, we have just ordered an MG4 Trophy (due for delivery end of July) and the dealer recommended these:
A simple solution to help you transfer to and from a car seat. The Transfer Board folds out next to the car seat enabling users to easily transfer over. When the Transfer Board is not in use, simply flip it up and fold it away, where it remains discreet ... Read More
www.elap.co.uk
There are other similar things available, but they might help your wife get in and over the sill.
Or another, much cheaper thought! My wife uses a leg lifter to help her get in and out of the car. There loads if you search for leg lifter on eBay - here is one example:
Find many great new & used options and get the best deals for For Wheelchair Mobility Tool Physical Therapy Foot Loop Rigid Leg Lifter Strap at the best online prices at eBay! Free delivery for many products.
www.ebay.co.uk