Can I make a suggestion? It isnt going to stop the hurt you feel but might be something to help a little in the future. I dont know if you keep a diary, but could you keep rather a notebook for your grand daughter. So you might write in it on her birthday, telling her that you are thinking of her, what you are doing, describing perhaps your garden or what you are wearing. Again on your birthday or christmas or any occasion that is important to you.
Dont make it a long note, or make it sound too sad, but if hopefully as she grows up , things may change or once she is older she can choose to be in touch with you, then the notebook would be something she could read. It would show her that you had thought of her all this time, and let her see what was happening in your life too.
You could perhaps have some photos of the garden, any pets you have etc to go with it. If you are a gardener yourself you might choose to plant something each year in her honour, and hope that in the future she may be able to come and see it. Perhaps you might choose to have 2 notebooks, one for her to read in the future, and the other a private notebook for yourself to write down how you are feeling at those times, and then put it away and try and go for a walk or have a swim, or anything physical to get through the difficult days.