You have a problem. This woman is lacking appropriate boundaries, and has found in you an accomplice for her inappropriateness. While Smartteen makes an interesting hashkafic point, it sounds to me like by doing what you are physicaly able to do (in order to get schar), you might lose your sanity! You did not mention whether this is impacting your Shalom Bayit, but I can’t imagine that it is not.
Here are two ways you might want to consider adjusting your relationship with this woman:
1) Gradually: the next time she asks a favor of you you can put conditions on it (ex: “Oh, you need me to pick up your dry-cleaning? No problem. i’ll be in that area Thursday and i’ll be happy to do it then”)
2) Cold Turkey – with the intent of coming back in gradually, if necessary: when she asks a favor of you you simply tell her that you’ve realized that all of the different chessed activities you are involved in are taking away from your family time, and you need to cut back right now. As soon as your household is over this hump, you will let her know. She may get more insistent, calling more often, to test you. Stay firm with your line that you will let her know when your time has freed up a bit.
Once she has stopped assuming you will always be there helping her, you can then decide if your want to offer something at your convenience (“I’m going to the bakery,can I pick up some Challot for you?”)
Perhaps this isn’t the definition of “true chessed”. I am looking at it from the poster’s perspective, as someone who is obviously not “shalem” with doing the chessed the way it is being requested of her. No one person can fill the role of a “Chessed Organization”. If this woman needs help to that extent, then she should be referred to an appropriate local Organization…