I've seen this before! Try this -- first all, obviously foreplay (which includes licking the kitty... quality *and* quantity time at the kitty is a must). Then, have her mount you up (woman on top, facing you). Let her ride with deep strokes, getting good vaginal stimulation. Initially she'll be riding vertically, but as she wants more clitoral stimulation she'll ride more and more horizontally. Now... since she has issues orgasming from normal sex, chances are a rock-hard dick will miss her clitoris even if she's vigorously riding horizontally (oh, and it can hurt your dick too!). Well, that's where you have to relax just a tad... yes, soften-up just a bit so your tool can bend enough so as to hit her clit when she's riding horizontally. Your dick will appreciate it too... you won't sprain it!
I know it sounds strange (since harder is always supposed to be better), but you may find yourself doing 3-4 cycles of this. She rides your vertically, you get hard as a rock. She then starts more and more horizonal movement -- that's your cue. Relax a tad, give her the flexibility she needs to hit her clit and then "handle your business"! If it doesn't fly, she starts riding you vertically again, you get rock-hard again, rinse, repeat!