Heaven knows I have little expertise in this, but maybe if she's uncomfortable with saying the words that you could come to a "code" behavior that she can use that will let you know what she would like. I had a friend who said his wife would always put a Hersheys candy bar on the top in his underwear drawer in the morning if she wanted to have sex that night ... something like that -- or maybe a particular action or noise during that would let you know she ESPECIALLY liked what you just did ... just my simple ideas .... hope you find a workable solution for the two of you.