well the only way out is to be honest......hey, I agreed to pick up your kid because I thought there was a crisis and it was a one time thing, but I have other things on my plate, I am not available to do this on a regular basis. she does not need to know that you don't want to do it or that you may or may not be available. she obviously assumes from your conversations that you have the time and generous spirit that she could just take advantage of you. you need to be assertive and set boundaries. you are not responsible for her financial and mental state. she does not have very good boundaries. that doesn't mean you have to take responsibility for them. take care.