Very likely that she will ask more when her request is granted everytime. Not that i don't allow her to have extra off day during the week but to start with one, there is always the next time and the next time, the same goes to other things too. Sometimes having a domestic helper (dh) at home is like baby sitting another child, their needs are not food, company, cuddle but day off, money, holiday.... sitting down to talk is very time consuming but this is the only way to solve a lot of problems, if there is no talk, I think I have changed one after another almost every year or every contract, something that i really avoid doing as it really takes money, time and energy to start teaching the new one all over again, baby to adapt to another nanny, and do not know what she will be like soon.....
We can only offer advise base on what you have written and our experiences with dh, but you are there to hear her story, so talk to hear and like Joannek said, don't promise anything too soon and if really needed, write it down to ask her sign. I believe things will clear out as the bright sun and everyone will have a nice and relaxing Christmas!
Have a good day.