Although many people might suggest that you simply stop doing the little things that she doesn't thank you for, I would recommend a more reflective approach.
It's unfortunate that your partner doesn't recognize your kindness. Before you act on your frustration, you might first take a step back and ask yourself WHY you do these little things for her. Is it because you care for her and genuinely enjoy doing small things that you believe make her happy or make her life easier? If so, then being thanked shouldn't matter quite as much. People who love one another often do things with no expectation of anything in return (not even a thank you sometimes).
Alternatively, do you perform these small favors because you're seeking her recognition, acknowledgment, and approval? It's not a bad thing if validation is a motivation for you. You just need to communicate to her how important acknowledgment is for you. If recognition is a key driver for you, then you need to have an honest, open conversation with her. Ask whether she even wants you to do these things. (It's quite possible she doesn't. That would be a plot twist, wouldn't it?)
Share with her why you do them and explain that you're the type of person who needs positive reassurances that what you're doing is valued and appreciated. She may not realize she's as thankless as you perceive her to be. Add that recognition of your efforts is the best way to ensure that you will continue to do these little things.
Based on your discussion, try to come to an agreement on what behaviors each of you will continue/stop/start.