There are lots of women out there like "your friend". This is a very common problem. I would second the suggestion Kegel exercises. You do these by tightening the pelvic floor. There are a couple of ways to learn this. You practice by trying to stop urinating in mid flow. That will give you the feel of the right muscle to use. Then sit on a firm chair with comfy clothing and do the same thing, only this time try to imagine that your pelvic floor muscles are like curtains that you are drawing together at the conter line of the vagina area. Try not to tighten your glutes or legs while doing this. It is natural for your lower abs to tighten somewhat. I try to get my clients to do 10 to 20 every couple of hours if possible. You can also just do a faucet exs in which you stop you urine flow 10 or so times every time you go to the bathroom.

You can also invest in this:

http://www.kegel-exercises.net/pwrx/...FSnKggodImi4SA

Or buy some of these, (please note the following website contains sexually oriented language, uses the word puzzy many times, so don't go here if your offended by such things):

http://www.lazygeisha.com/mediax/geishaballs.pdf

Now you might think I was joking when I posted that. Although I find the wording of the website quite funny and silly, I actually mean it when I say that you can improve pelvic floor strength by using smartballs or ben wa balls. Smart balls are easiest, and you do want to leave them in for a while (20 to 30 minutes) while standing so you're muscles have to work to keep them in. When that's easy you can progress to ben wa balls. These are much harder to hold in while standing. You can buy these items at a sex shop and they aren't that expensive.

And... you might even get some nice side effects from using them.