You are only being taken advantage of if you let yourself. I imagine that enough “no, I can’t” when she asks for a switch, will lead to her not asking anymore. You can’t make her stop asking. But you can say no. And if you say no, you aren’t being taken advantage of, right? Because it’s your decision. And if you want an explanation as to what she Is doing since you are making your decision based upon that whether or not, she also has the choice to not tell you with the consequence of you saying no to her request.
Boundaries took me a while to learn. You can’t make someone act a certain way. But you can decide what you are going to engage in. And if you chose to say no, that enforcing your boundaries If this is indeed a boundary.
And when you are divorced, first right of refusal is written into your agreement. The parent always gets the first choice, and if the answer is a no, then the custodial Parent seeks an alternative .
In summary. You don’t get to decide what others do or say or offer to tell you. But you do get the right to say no.