If she has little fat, I'm not sure you'd want to switch to micros. I had the problem with fat and switched away from reg. sof sets (this was b4 micros were available) to sils just b/c of that problem, then I tried micros but if you have little fat in my experience, sils were better, BUT not great. I ended up using rapids, yes, it would help to have more fat to push the needle into, but you won't have muscles crimping cannulas, and also, rapids are extremely comfortable..I use the 6mm, and that's the same length as the micro, if she's thin, I'd suggest first trying the 6mm, even though the rapids come in 8, 10, and 12? also I think.