I think your provider is just trying to maximize her income. If you can commit to certain days/week and pay that flat fee so she can fill around you, why is that a problem, especially if you will actually be playing less than what you are now? I think this provider has been bending over backwards for you and has had enough. She needs to make an income just like you do. The fact that you were her first client explains a lot. She took you on and accommodated your hours like most of us do when we first start. Now she is realizing that to make her business worth running, she needs to run at capacity and your casual hours are standing in her way. If you have such issue working with her on this after she has been flexible for you for so long, then you might as well look elsewhere and good luck finding a provider who will accommodate you like that.