One additional thought: Next quilt, ask her, "I know the past couple of quilts I've called and inquired about, so I was wondering if this is a problem? How do you manage to keep up with the due dates? Does it bother you/when would you like me to call you if it's late/almost due?"
Start this conversation. It's worth it if you're happy with the work and price, and only have concerns about the turnaround time. It's a normal business discussion, and no one minds having it. I feel certain, since this has happened twice now, that it's a conversation she's had more than once...and probably doesn't mind (else I'm assuming she'd schedule better, call customers if delayed, have a better system for managing time, etc.).
I wouldn't mind it at all. I don't quilt for others, just for charity and myself, but have many friends who quilt as a business. This conversation wouldn't upset them at all. They'd prefer it, certainly, to loosing a customer!