do we have to take the daughter of my partner on every holiday ?

My partner has a 5 yr old daughter from a previous relationship and the mother has custody and we have visitors rights. We now have a 2 month old daughter and have taken a small holiday away and the mother of the 5 yr old has said that in future we are to take the 5 year old away with us on all holidays as she is part of the family. does anyone think we should have to do this all the time or just occasionly