No no no, she's not lowering the effectiveness!
I assume she's starting her period sooner in her off-week than you do, and so she has several "blank" days after her period is done, but the new on-week hasn't started yet, so she's putting a new ring in sooner - ie she's off the ring for less than 7 days.
Honestly, I see no problem with it. You'll use more rings a year with way, but other than that, it doesn't seem uhealthy! It will not decrease the effectiveness.