I am not quite as small as your wife but always have trouble finding gear small enough. I am 5'4" and range between 116 and 123 pounds. I have a Zeagle Zena for recreational diving--very simple. no pockets or extra mess, and it is a VEST with zipper rather than a cumberbund with buckles. It is designed for a woman's body--small waist, wider at top. I also have an AquaLung Pearl, but I am NOT impressed with the quality. It is designed for a woman's body too--it is made to fit like a sports bra--flaps cross the chest instead of buckles cutting across it. Aqualung also makes a travel BCD that is light--something like the "Lotus."
If youa re talking about tech diving, I was just given a TINY Halcyon aluminum backplate as a gift. It is extra short since the standard back plate will cut into the lower back/ hip bones of a shorter or narrower person.
Just make sure your wife TRIES on the gear before buying it and MAJORLY IMPORTANT--have her try it on with TANKS attached b/c my biggest problem is that the tanks hit me in the head, especially if I use a BCD with two straps (ie the Zena). If the set up bothers her, she will not dive with it--so buy with care! (Or sell me what she doesn't use cheap!!!) ; )
Let me know if you want more detailed info.
Ariane