crafty_linda_b nailed it. It's likely not HER but your DH who's brought this problem on; I mean, how did she find out you know how to use a sewing machine anyway? :D
So, encourage HIM to resolve it. Tell him what you've told us. Remind him that nobody asks Picasso to paint their garage door, or Georgia O'keefe to do a mural on little Jenny's bedroom wall.
If DH is getting the "little projects" from this woman's husband at work, and not speaking to the woman at all, then that's an easy solution. Men rarely have the emotional hangups around "confrontations" that we women do, he can easily tell the other Dh that you no longer have time and it'll be no big deal, I'll betcha!
Jan in VA