I usually go by the time that I got them up. So if she eventually went back to sleep and slept to 10:30 (which is really great that she'd do that on her own, BTW!), then I'd put her back down at 1:30. Or if she seemed a little off, maybe I'd split the difference and try for 1:15.
I just reread your post, though and saw that you're concerned about the catnap. Maybe put her down a little after 1, but before 1:30 and see if that's a happy medium. Such a guessing game, isn't it?