Here are a few real life scenarios my friends and family in blended relationships have had to deal with:
If, during the teen years and the (very common) stage of arguing with her mum, his daughter decided she wanted to live with her Dad and only see her mother on weekends, how would you feel?
She wants to play music loud, have her friends around on a weekend, which is a normal teenage thing to do, and a sleepover at least once a month. Does that work for you?
As soon as her father moves in, your flat or house becomes her home. Not a place she sometimes stays, her home for part of her life. Are you comfortable with her treating the place like somewhere she’s entitled to be? Can she browse the fridge and look for snacks, have a bath for an hour, fill cabinets with her stuff?
Who is responsible for cooking, cleaning, washing her clothes, picking her up from school if ill, looking after her on training days that fall during her time with her father? Especially if you WFH?
Is she welcome to stay until her mid twenties as she struggles to save money for her own place? Do you and her father agree how long is long enough?
Dies she go on holiday with you?
I’m not judging either way. Everyone has their own boundaries. However, if my friends and cousins had held these conversations before moving in together, some acrimonious situations could have been avoided.