Yeah sometimes customers can be a real pain when it comes to extras. I do some things for people. i might take out the trash can or grab their newspaper, help move something ect. usually i don't mind when it's something quick but when it's spreading bags of mulch and trimming i just wont do it for free. It's not worth it and if you do it she knows she can ask for more (given your description of her).
I've started to learn this year that some customers arent worth the money they pay you. The kind that you gave a good price too, do extra stuff for, free of charge and when it comes to big ticket work like trimming or clean ups they have little billy from down the road do it for $20.