Thank you to everybody for talking me out of jumping off that ledge. I do think I have to find a better way to set boundries so I am not continually used. I have to stop doing favors. I don't mind helping out a person from time to time but it seems that when I do anything as such, her disrespect goes up and her expectations go up also. I am sure that I will be asked this afternoon to bring S4 directly to her place, as it happens every other Monday when he goes with her. I think I just don't have the time today and will stick to our agreed upon location. Start small with not accommodating her and see where it goes.
It's tough, but there IS a difference between a boundary and a punishment. I think you need to determine the lines that you do not want crossed around you, and then set expectations of consequences that you can and will uphold. Dont get hurt and then go around retaliating at random.
Certainly reasonable not to accommodate every one of her wishes. Just dont be a jerk about it.