I can tell you one thing. If I were your daughter, I would want to know sooner, rather than later. Someone else already posted that the most important thing you have now is time. It is time where you can make cherished memories for your family.
Maybe take some of that time to write letters/make videos, to your baby granddaughter. Tell her stories about her mom. Tell her stories about you and her grandfather. Tell her the things you would tell her if you were there with her while she is growing up. Because you will be there with her, through your daughter, your husband, and everyone who is close to you. But to be able to read/hear your words, that will be priceless to her.
I will be sending you every positive thought and energy that I can. I wish I could do more. 
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