I don't think injecting in the femoral vein as a regular access spot is an option. It's right on par with injecting directly through your temples in my opinion - in other words, not realistic at all.
I mean, maybe once or twice, but you really think the OP cares much about one or two more shots? You think now that she knows about femoral injections, she'll be good to inject cocaine for a few more months with little issue?
Injecting there is just asking for trouble, way too much trouble. Sure, go for it, tell her how it's done. But 1, I don't think it's that stage for her and there are many other places she can hit, and 2, femoral injections for recreational and regular abuse is just not safe at all. Not at all.
Best approach is to recommend using other sites. Even re-using some of those banged up spots is better than to try hitting the femoral. But if it came to that, just fucking quit. Seriously, femoral injections isn't something you can carry on for more than a week.
edit: don't get me wrong I'm all familiar with risky things we do to get high, and I know the lengths we have to go to. Re-using cottons, sharing needles, all sorts of stuff like that. But there's a line and femoral injections as a regular activity (as opposed to just once) is definitely crossing the line in my opinion.
The OP should definitely look into butterfly needles.