You sound like a very kind and thoughtful person and it is wonderful that you are adding assertive to your list of strengths
I personally get so frustrated by people who insist that every aspect of life get turned into a competition
“You have more money than me so I have decided that I don’t need to pay for X”
“You have more free time than me so I have decided that you should spend it running around after me”
“You are not stressed in the same way that I am so I have decided that your causes of stress aware invalid”
I think we all agree that if someone is abundant in money, time, emotional well being etc etc and as a one off can’t show an act of generosity then it is frustrating and we might have a moan, but even then it is their right to do as they please
I empathise with you on so many levels, keep doing what you’re doing. You have not withdrawn help. Reiterating to her what the new terms are is part of being assertive, just don’t fall into the trap of excusing your decision
Personally I have discovered great power in learning to stop trying to justify my perfectly reasonable actions
For any 30 Rock fans “Say no. Keep it low. Let her go”