My dogs are driving me insane i stg

Our newest dog rosie has taken a liking to bella, and bella seems to like her as well, but the problem is that rosie is smaller and has small dog syndrome, shes not agressive, but she tries to act dominant with bella, but because bella is almost twice her size she keeps failing miserably, and even then she cant quite figure it out. Like she'll start humping bella mid play and just hump herself away, literally. Like a week ago she started humping bella and just kept going by herself f rom the edge of my bed to the wall and i just sat there like bro wtf are you doin 😭