when service isn't service (ignore the grammatical errors, i am venting)

according to a recent poll on some pointless gossip website an astonishing 77% of readers said that they would rather grant custody to kevin federline than britney spears. and i was among that 77%! hath hell frozeneth overeth?

anyway, i am in need of some serious advice/reinforcement/chocolate cookies. recently, i was chatting with a sister in the ward about life with a newborn. she was saying that she was in school and also trying to work part-time and money is tight. i offered to help her out if she occasionally needed someone to watch cameron, her 2 month-old son. i said something along the lines of "i would love to help you out sometime, give me a call if something comes up." being a young mother, i am all about trying to help other mothers out. however, this sister, who we'll call, chutney, seems to think that i am now her permanent babysitter. last week, i watched her baby 3 times for about 3-5 hours a shot. the day i watched her baby for three hours, she ended up staying at my house an additional 2 hours to discuss her life including all sorts of things i didn't need to know about anybody, let alone a nearly perfect stranger. chutney always calls the night before she needs a sitter, regardless of how long she knew about her work/school schedule. plus, she always fudges on the amount of time that she needs me to keep cameron. often she'll say, only about two hours, or whenever her husband gets off work. i honestly think that she is lying to make the amount of time not sound as long as she really needs. she is married, but i guess her husband works full time, including saturdays(???) and is unable(unwilling?) to help. and she often mentions that he is a non-member and wants to make a good impression on him with the Church. if find that very sketchy and manipulative towards me. after last saturday's never ending babysitting appointment, i vowed to myself that i was taking at LEAST a week off from watching her baby and after that once a week at the most. on her way out the door, chutney told me her work schedule for the following week and i didn't say anything because i didn't think she was implying that i should write it down and be prepared to babysit. well, i was wrong. she left me two messages on Presidents Day, once to ask if i wanted to go to lunch and then again later to see if i could watch her baby at 7:15am the next morning because she had class. i never called her back. i should have, but i really didn't know what to say to her. i even made thomas practice some "role plays" with me so that i would be prepared to tell her NO in the future. then yesterday she calls me again and wants to know if i can babysit today because her husband is sick. when i tell her i can't because i need more notice, she then gives me a guilt trip about how her husband is throwing up and she doesn't want her baby to get sick too. i don't take the bait and i just said it was too bad for her husband. plus, she already told me her work schedule for the week and she was going to need a sitter for today even if her husband wasn't sick. PEOPLE!!! i have been sick before and i still take care of my child!!! she sounded REALLY annoyed with me and i wanted to be a jerk, but i cannot allow myself to act like that towards her. then TODAY, when i said i was going to be busy all day(i have been, it has been 73 degrees and sunny so reagan and i played in the yard to our heart's content and then we went and threw pennies in the local wishing well) she left me a message again to let me know when she would need me next week, so that i would have "enough notice"!!! excuse me, do i work for her and not know it? by her calling to let me know when she needs me, is that her asking me or telling me? am i on call for babysitting just because i offered to help? does chutney think that because i am a stay at home mom that i don't do anything but watch TV all day and can watch other people's kids at the drop of the hat? bytheway, i have my own very active almost 2 year old and i am 5 months pregnant and i have my own life!!! she doesn't pay me, and i don't want money anyway. i rarely get a thank you! i want her to get responsible for the life she is living and for the child that she brought into this world!!! GGGRRRRR!
so, this is what i want to say and please tell me if it is forceful enough, civil enough, well worded, and understandable to someone who doesn't understand basic socialization. i can't just avoid her because i will see her on sunday.
"chutney, i understand that you are in need of long term child care and unfortunately, that can't be me. please look into day care or a permanent paid babysitter. or please call our relief society president and see if she can help you arrange some additional help from other sisters in the ward." ideas???