I would just be honest with her and tell her you are not ready right now and maybe some day you will be ready. You need to think of YOU first. I would just tell her that you would prefer her not to write and you will write when the time is right for you. I am so sorry to hear about your mom passing away. I will keep you dad in my prayers...
I know that your decision is not easy to make but if you are not ready, she will just have to understand. I am sure it will probably hurt her but she just needs to give you time..
Good luck to you..Congrats on your children..
Hugs,
Cathy