Personally, I can NOT see myself mentioning to a CLIENT that they should trim their nasal hair and how to go about it.
I mean... I'm sure that they realize it's there and all that. If they're unconcerned, then dont wrack your brains about it.
Odds are, if you did say something, no matter how you put it, you're likely to offend them and risk losing a client.
The only person I think I could honestly suggest a nasal trimmer to, is my father in law. I also tell him to 'mow' his ears LOL
If someone said anything remotely like that to me, I'd probably flip out.
Also, if it is something that they haven't noticed, then you point it out, you may end up paranoying them and upsetting them a great deal. Embarassing them. Last thing you want to do is that.
Sometimes, our personal opinions really need to be left at home.
And I wonder why you think it's holding her back? that's the oddest thing I've ever heard to be honest.