I know exactly what you mean and it is normal to think that feeling better would mean you are forgetting her. Not everyone experiences this but many people do. I'm struggling with this thought too and was just reading about it this morning in one of my books on grieving. Have you tried writing down the happy memories that you have of her? or maybe making a collage of pictures to remind you of the good times? Doing something like this might help reassure you that you aren't forgetting her. I've been keeping a journal of memories. It's only been 3 weeks since I lost my baby Jasmine and looking at pictures is still too painful for me. I know one day I will be so grateful to have them though, once the sharp edges of my grief have softened.
Have you considered counseling? It might help you to talk through some of this with someone. I'm looking into grief counselors in my area.
I miss you every minute of every day, my sweet baby Jasmine.