Am about to lose my mind!!

I have a 2 children in my care..one is 31/2 and the other is 14 months. I have a signed contract stating 3-days 7-4:15 and 2-days 10-5:45. This week is all 10-5:45. I asked her to pick up the kids at 5 on Tuesday and Thursday because we had a planned work bbq and Thursday we have my sons meet the teacher on. she only accommodated me on Tuesday not Thursday...texting me saying she couldn't on Thursday quoting"normally it wouldn't be a problem but people suck..LOL" (text). She always pick the kids up at 4:30. Its just frustrating because I have things that I have to do and feel like I am being taken advantage of. they treat me like I am suppose to be at their beck'n'call...I know I should grow a backbone!! Advice???

Do you have a set schedule with her? For example Monday, Wednesday, Friday are until 4:15 and then Tuesday and Thursday is until 5:45pm or does it change depending on the week?
Do you have a set time frame that clients need to follow in regards to time changes needed for care?
Do you have other children in care, or are these your only clients?
All these things will affect how you can proceed, in my mind.
My advice to you is to talk with the client and enforce your contract regarding hours of care. Let her know that regardless of your hours, these are the set hours of operation as you have a life outside of daycare and need to plan accordingly. Also, if she is late, then set a late fee. Make sure it is inconvenient for them.
Also, if she needs to change the hours, for what ever reason, she needs to give you 24 hours notice, so you can let her know if you are available or not.
Do you have a handbook of policies? Maybe you need to review and make some amendments that all families must sign.
Hope that helps you out some what. It is not a nice feeling when parents take advantage of our services.

I don't have a set schedule..she works at Shoppers so her schedule changes. But from talking to you and another person I will be amending my contract!! Definitely!!! Thank you so much for your suggests!!!

Yes, even working at Shoppers, she should know her schedule at least two weeks in advance, so there is no reason why she is changing her schedule at the last minute on you.

Good luck!