Sorry but I can tell just from the mobo picture, well and the model. All of the M4s from Asus were AM3 mobos, not AM3+. The FX series will only work on AM3+, while Phenom II/Athlon II will work on AM2+/AM3/AM3+.
The best way to tell if your mobo can support a FX, besides the CPU chart from Asus, is the color of the socket. If its white, it wont. If its black it will.
Looks like the best CPU you can get your wife is a Phenom II X6 1100T, and honestly thats a better performer than the FX 6 core anyways.http://www.newegg.com/Product/Product.aspx?Item=N82E16819106012
Same price and overall it will perform better. Remember the FX series are not full cores. They have modules which act as about 90% of a full core overall. So the 6 core is more like a Phenom II X4 in performance than it is a Phenom II X6.