Right of First Refusal

My partner and I have been together for several years now and I live with him and his children whom he has a little less than 50% time. When I have picked the children up from school or stayed with them for a couple of hours during his custodial time their mother has claimed that she has right of first refusal even though it is not written in to their separation agreement. Can she do anything to prevent me from doing these things for our family during my partner’s custodial time? And would our being married change anything about what she could protest about the times I am with the children with their father not around? Thank you!

If it isn’t in the agreement, or court order, if it is his time, then it is likely his time to do with as he sees fit, so long as the children aren’t in danger.