I would first try putting a sippy of water in her crib with her after she goes down for the night. When she wakes up, she'll find it, and if she's really thirsty, she'll help herself to it. I would also suggest putting her down before 8. Try 7:30. You may find that an earlier bedtime causes her to sleep later by itself.
If thirst does not seem to be the issue (which is probably isn't) I'd let her cry. DH and I have a rule that we don't go in to get DS before 6am. There are days where he cries back to sleep, and also days where he sleeps till 7:30.
Our DS (12 mos) is transitioning to 1 nap. I have found that on the days he only has 1 nap, he sleeps later in the morning. We put him down at 7:15 nightly.
I would not try to force your DD into 1 nap, though, if he's not ready for it. She'll do it when she's ready, and you'll have a much easier time of it.