haha, this is very old but I will answer you anyway...
I am Spanish, also highly educated, and despite have been living in Uk for the last 4 years, never say thank you unless I consider it is a favour you are doing for me (normally because I have previoulsy asked for it). So, if cooking, laundry, lift, are done by you just because you are willing or is part of the agreement on which her accomodation is based on, she probably does not see remotely the need of saying thank you or any acknowledgment whatsoever.
It's not just Spanish. It's also French and German. We massively oversay "thank you", but seeing as your student is here to learn English and part of it is to learn customs, too, not just the language, you should point out to her (in a joky way) that she needs to say it.
I have experience of this myself and you just have to steel yourself (in a very non-British way) to say something. It's for her good, too, because if she is in a more formal situation and doesn't say "thank you", it could be detrimental for her.