When you figure it out tell me

Maybe try put the cot mattress on the floor next to your bed. That's what we do. E sleeps down there most of the night. She will not have a bar of the cot.
Once she is in a deep sleep I just slide her over to the cot mattress. (though we are also sleeping on the floor at the moment but you could do it with a single bed? making the bed bigger and room for everyone?)
We're thinking of getting a toddler bed too or putting her into sleep with DD1 because she loves to cuddle up too.
She slept two nights on her own in her own room on mattress on the floor then the stupid molars started coming through so we are back to co sleeping and one grumpy mumma from lack of sleep.