I am not a fan of twist-shifters. One winter I rode a bike with twist shifters and had wrist pain all winter that took months to go away. It has never come back since I sold that bike and have stuck to either flat bar or drop shifters of the conventional styles.
I absolutely think that the first priority has to be a frame that fits her, but if she is not too short or too tall, the bikes with flat foot technology might be a good choice if her hips are affected.
There are advantages to internal-geared hubs for commuting, most importantly the ability to shift gears while stopped. The Dual-Drive systems combine a triple chain-ring with an 8 speed IG rear hub, giving 24 gears, but still allowing you to down shift from a stop.
There is a trade-off with a front-suspension, you do lose some power, so it is important that your gearing makes up for that.
Another option to consider for brakes would be disc brakes. If she is going to commute in wet weather, they are ideal and I feel they require less grip strength.
Finally, don't count your Dad out completely. Get him on board in researching the available options and what might work best for her special needs.
Bikes I would suggest looking for
http://www.breezerbikes.com/index.cf...TOKEN=81605061
especially the Town bikes and new Finesse
http://www.giant-bicycles.com/en-US/bikes/lifestyle/
especially the Suede and Transend series
http://www.civiacycles.com/civiacompletebike.php
if she thinks she could use a diamond frame, like the Suedes, this comes fully dressed
http://www.electrabike.com/04/bikes/...06_twn_15.html
the Townies tend to look like they were designed for a little girl, but this isn't too bad if you add your own fenders