Maybe a safe co-sleeping solution for you might be a matress on your bedroom floor. If Alexa can see you right near her she might find it easier to relax when she wakes at night. I find with night waking that if either of my babies have time to get stressed thety wake up more and are harder to settle but if I get to them quickly they re-settle much faster. I think that when you sleep in the same room as your babies they wake up just as often but when they see you nearby they're reassured and go back to sleep. Later you could try moving the mattress to her room. Alternatively you could get a bed for Alexa's room and sleep in there when needed.

Yasin didn't sleep through until he was over a year old and he still wakes in the night so I know how you feel. We just kept experimenting until we found a solution. In our case it was to get Yasin a double bed so that we can co-sleep with him as needed.