NO such thing as a miracle diet pill. Zantrex and all the other OTC stuff may hae slightly different recipes, but they generally just boost "fat burning" a tiny bit more than diet & training. But given that, they don't make the difference. Also depending on each person's own body chemistry, they may or may not experience anxiety, shakes, headaches or just nothign at all from the different thermogenics.
I think the first and only relevant question is, does your wife already have a tight & solid diet & training program that she is gettign results from? If not, spend your time on that first. Any pill is only a SUPPLEMENT to an already solid program. Don't expect miracles because they don't exist. Anythign you try to force your body to do that your diet, trainign & lifestyle don't already support is going to either do nothing, slow down any progress she's already made or will work for a short period of time & then rebound probably worse than what you started with.