I just had a baby and I was extremely unsuccessful transitioning my oldest into a crib. It actually created separation anxiety (even though his crib was right next to our bed). I would say it’d be easier to have new baby get used to sleeping solo from the get go but that personally didn’t work for me since I exclusively nurse. If it helps, I now bedshare with both of my babies! Baby on left side, me and dad in the middle, and oldest baby on the right next to dad.
Maybe put a mattress in her room to start to transition to using her own room more?
I’m right there with you. We’ve been co-sleeping as well and I’m due in two months. I don’t really want to stop because sleep in our house just hit a plateau where everyone actually gets a decent amount but at the same time I don’t want to co-sleep with a newborn and a toddler