Daughters new phone is changing my contacts and vice versa

New phone for my daughter so starting from scratch.

all of her contacts are on my phone and when I change one or she changes one it then appears or changes on both phones

she has her own Apple ID as do I, we have family sharing but we have had phones for all the family for years including her and I can’t figure out by changing this one phone all her contacts are on mine and when I delete them they then delete off her phone.

as I said we have completely different Apple ID but we have family sharing with all the family (2 adults and 2 kids)

driving me round the bend!

any help would be good before I end up calling the wrong person as some names are the same as my co workers etc