I would say that when "i" make the coffee, "I" obviously make it how "I" like it. I would then tell her that I'm not Starbucks where you place an individualized order for each cup. I'm not a mind reader nor do I even have a memory which allows me to make coffee to each and every persons specification. In closing I would inform her that she's welcome to come in earlier and make coffee how she likes it. I would also tell her she's welcome to stop off someplace before work and order coffee and she's welcome to bring me Vanilla Latte when she does so.

You really do need to be direct with some people. Not everyone appreciates a direct approach but they usually learn you won't be a doormat pretty fast.

I've dealt with women like this myself and it's such a pain in the butt. I'm a recovering doormat myself so my heart goes out to you. Stay strong.