I'm not really big into cummig in my wife's hair but she lets me do it occasionally. She doesn't worry about pre-cum but I don't produce a lot of it either. If I do I just wipe it off with a tissue and keep enjoying her hair.

Sounds like she puts a lot of work into making her hair perfect so you're going to have a hard time convincing her cum is not bad for hair.

Instead of wasting your time and effort on that, why not just solve the problem of cum in her hair by getting yourself a box of unlubricated condoms and when its time for the hairjob just roll one on over the head? That way you get to feel her hair on your shaft and balls (where it feels best IMHO) and she doesn't have to worry about getting anything sticky in her perfect hair. The other alternative is for her to wrap her hair around your shaft and keep the head in her mouth.

Let us know what happens.

Good luck.