Does she say thank you? I really doubt that shes gonna come clean your place to show her apperciation. And I almost feel its silly that you expect that....
She should be greatfull that you help her, and you should feel good that you can help your fiance out. But as long as she says thank you and is sincere that should be all you need.
Now if you want her to do things for you because you want her to make you feel special that is a different situation all together.
If you want her to clean or cook cuz you gave her money you are no longer doing her a favor, you are now paying her for a service.
You should give her the gas money and be happy your a good fiance. Then you need to talk to her about the things you would like her to do for you to keep you happy and feeling apperciated in your relationship. This should have nothing to do with the gas money you gave her.