That's the other option... If her midday nap has been crappy and interrupted, then put her down for her afternoon one earlier than normal.

If I want to go out, during one of the sleeps, then I make sure the other major one is a good one. Does that make sense?
If he has a terrible morning sleep, then I'll stay home for the midday one that day. I find that at least one of the 2 big ones needs to be in his cot, and for the sake of sanity at bedtime, I try to make sure we're home for his afternoon nap, or at least in the car for a full hour (he generally sleeps there).