L.A.
How can you break the cycle? She is two! She is growing and changing every day. Don't expect her to remain the same, either with sleeping, eating, behavior... two is a busy time both internally and externally. It sounds as if you have been very lucky until now. This is not a discipline issue. Be a mommy, regardless of what time it is. You have gated her in - she cant even come to you when she wakes up, so you need to do what mommies do and go to her. Better yet, get rid of that gate.