Wow - this is a really touching story. Unfortunately, there aren't any details about height, years working out, clothing sizes etc.
Does she work out - not just cardio but weights? (I hope so!)

How long has she worked out? Lifting will boost her metabolism (safely) and provide a muscle base that will be very useful to her in the future.
I would DEFINITELY avoid any fat burners or clenbuterol etc.
DEFINITELY avoid any sort of sedentary lifestyle!!!
Manage the weight with a good healthy diet plus a good set of immune-boosting vitamins and also ensure she gets sunshine in moderate quantities for vitamin D.
Another trick in your location is to ditch the car and ride a bike. This is way better than taking any fat-burner in my opinion. I believe that you and your wife are in a good city for bicycling. (bad parking, very high gas prices, pretty good weather, and many bicyclists so that the drivers are alert to bicycles on the streets). She might enjoy this blog from the City that the Starship built (music reference:
http://www.youtube.com/watch?v=TxGGckAc1rs).
http://velovogue.blogspot.com/
(more bike culture from the city where gas costs more than $4.50/gallon):
http://www.cyclecide.com/
After she's worked out/bicycled for maybe a year (in her case as HIV+), I think she might be a really good candidate for something like anavar or NPP. (Of all people, she probably needs less justification than just about anyone else for taking anavar, even if it's off-script).
By the way, I'm assuming she isn't obese...but just wants to build muscle and reduce fat levels with an active lifestyle.
Intellectual curiosity:
Is your ancestry from somewhere like Sweden, Norway or Denmark? From what I've read, the small percentage of people who are HIV-resistant have ancestry in _northern_ Europe. The frequency of the gene is a lot lower in Germany and points south and west).
Best wishes!