Rebuilding my castle...foundation is halfway...

[Lifes Twists]

I would say do what you are comfortable with. Given he did send you one on mothers day I would consider a simple reciprocal. A simple Happy fathers day with no happy face or anything. I went over two years until this morning without her recognizing anything. It was nice to see a simple Happy fathers day from her. You just have to decide how you want the interaction to go now and for the future and set the example.