30 notice policy????

I am currently boarding at a facility while I wait for spots to open at the school for the horses.... I have finally got spots at the school and have told the owner of the barn I am picking up the horses and said they will be gone in a week..... I will be paying for the rest of the month that I won't be there for... but then she has told me that there is a 30 notice period for taking the horses, so now she is charging me an extra $500 for the next month that will not be there for..... she has known the whole time that I did not know when I was going to get the spots at the school and was leaving when I got some..... she has never mentioned to me about the 30day notice but says it's on the borders agreement...

Has anyone had this problem or have even heard about this????