As usual, I would first ask what her doctor says (not what her yoga teacher says.) I am a bit confused by the focus on the hip if the problem is the kneecap tracking. That could be due to a tight IT band, but also many other things. So, second question: what is causing her patellofemoral syndrome (which usually refers to a mis-tracking of the kneecap.)
Have you seen the old YouTube video by Doctor Jo
? I found it interesting, even though it is a series of yang exercises.
To answer your basic question though of how to work the hips without stressing the knees, yes - it is possible. Flexion of the hips can be done with Caterpillar; Extension with Supported Bridge or Seal. Would she be comfortable with Dragons? That could also do extension. Abduction can be done with Straddle fold but maybe not Butterfly. The more challenging directions may be internal and external rotations. Maybe Butterfly can work for ext. rot. and maybe windshield wipers for int. rot, but go slow with those. Try a little, and pay attention!