I hardly ever post here these days but reading this made me swell up with anger. What a presumptuous ass this person is. Ugh. I have found that in the last two years since my son died it is the "godly" and "righteous" who have said the dumbest, meanest, stupidest shit to me. It is so easy to sit in judgment of someone when not living in their situation. You are doing the best you can and your children are not somehow suffering because you are grieving the loss of their sibling. Shame on this person. I'm sure God is really, really, proud of him/her.
Honestly, I think people need to know that saying those types of things are hurtful and ignorant (unless the sender also has dealt with the grief of a dead child, which I seriously doubt). I would absolutely send an email in response. But I think your husband is right. Wait so you can compose something with a measured response.
Sorry.