OP I am sorry for your loss.
I would gently suggest that expecting her to apologise spontaneously, when you didn’t make your displeasure clear at the time is a bit unreasonable. Either she has realised she said something stupid and may think the best option is kit to bring it up again in order to not upset you further. Or she doesn’t realise.
Yes it was a stupid question, but at the same time it’s only a question. That is actually better than making assumptions. (Like assuming it is too soon). In a way, she is allowing for that conversation and suggesting there is no shame in it. Some people (especially men) do start new relationships very quickly, and I don’t think it’s right to judge about that. She is trying to show an interest in how you are doing and where you are in the process.
I think it can be hard for people to get it right when someone has gone through crisis or tragedy. And we get very little steer from most people. I don’t think it is massively fair to dismiss a good long-term friend for saying one thing, once, which didn’t land well for you, without you expressing your feelings and giving her a chance to fix it.
so, I would either forgive now, or have a conversation - either proactively now or reactively, if she ever goes in this direction again. Say something like “I know I am nowhere near ready to move on, if I ever will be. Please don’t bring that up again- it feels really mis-attuned to how I am feeling. I know you want to be a good friend and support to me, so here are the things that would help me in this phase: x, y, and Z.”