Sounds as though this is a gig you'd say no to if it were just a business decision. If this is something I wanted to do as a favor and the pay isn't likely to be significant, I'd consider two paths:
1. Do it for free on a just-this-once basis. Less likely that the artist to ask you for a whole string of low-money jobs than if you do it as a favor at a far below market rate. Also, more likely the artist will try to learn what she can about sound reinforcement on this gig if it's clear you won't be riding shotgun at future gigs.
2. If it's an act with a low channel count playing a gig that's too low-rent to get shopped to any sound company, I'd consider putting together a robust but dead-simple mini-PA out of your extra gear locker, getting her checked out and dialed in, and then either loaning or renting the rig to her. That way, she'll sound better than she would otherwise, she'll learn a little bit about sound, and your time investment is much more manageable. I've done this more than a few times for young musicians, just in the spirit of paying it forward.