Help! 15 month old turns 3am into conversation hour

For the last month my 15 month old went from sleeping through the night to waking up at 3am and has conversations, sings, claps basically everything but sleeping. Sometimes it lasts 1 hour sometimes 4. Last night she was practicing shaking her finger and saying no no mine over and over again (she fights with her older sister over toys). I don’t know how to get her to stop doing this. She wakes up the whole house. I’ve tried leaving her in the crib alone, I’ve tried putting her in my bed with me, I’ve tried laying down in my 3 year olds bed with both of them bc they’re now both awake so I have to get both of them back to sleep. I don’t know what else to do. I’m exhausted and pregnant with my 3rd and can’t keep doing this every night. Someone please help me figure this out. I’m desperate!