Can a non custodial parent be held to certain boundaries for being to intrusive?

My husband and I have had custody of his children for the past 6 years, after disappearing for 2 straight years, his exwife has a one day a week visitation, and 2 phone calls during the week, our problem is she is showing up to their son's recreational activities after school. Not an organized sports league which we know she has a right to attend. but an after school basketball club, is she allowed to show up there anytime she wants and go to practices to organized sports on a daily basis or is she being intrusive. We feel our time is our time and hers is hers, that the normal routine of our family is our responsibility and she should respect that, she says their her kids and as long as they like her there, there is nothing we can do. What are the boundaries are there any, she has no respect for our family unit.