Whether it is you or your friend with the husband who is crap in bed, I would say the following.
I have been with my dh for 14 years, and it is common both to evolve and want to try something new, and sometimes to become a bit "stagnant". Wanting to spice up ones sexlife is a good thing, and it is a pity that she feels uncomfortable bringing it up with her dh. It is normal for ones sexual relationship to change after childen, and being with eachother a long time.
My dh once said to me years ago, and he was very embarrased, that he would like to try new positions, as he was becoming abit selfcounscious things were stagnant. I think that part of maturing together and evolving as a couple is to be able to recognise this and make changes accordingly. What am trying to say, albeit in a sort of roundbout way, is that your friend should not be ashamed to bring it up with her dh. He might even be relieved that she does. The way around it cold be to say something like "you know, we hve been with eachother a really long time, and I remember how excited we used to be about sex. Maybe it is time to try something new, and explore eachother again?"
People change, so why should they always want to do the same with eachother sexually? Get the Kama Sutra maybe, look at it for a laugh, say: "Hey, maybe we could try that?"