I'm sorry for your loss - so hard. Losing a son must be the hardest thing to go through.
To have this woman make life harder on that day ... so unpleasant.
I would leave it up to your husband to deal with. Nowadays, that's the standard. I think in the past, women felt they had to deal with their husband's families - not so any more.
Men deal with their own families. Women deal with their own. So he sets the boundaries for you as a couple.
On the day, of course you were overwhelmed with grief and that would have just shocked me and I would not have known what to say or how to have dealt with it either. I'm sure she 'meant' well - but it was not appreciated. I suppose if your husband were to say something to her, that's what he would say.
Sometimes very zealous people go off like that, and perhaps she has some mental health issues that caused her to react that way at your son's passing.
The thing is, now it is in the past, I'd just move on. You don't need one more thing to carry around with you. Let that go, so you can just mourn the loss of your son - and grieve and don't confuse this woman's actions with part of it.
Just let your husband deal with her, and forget about her. I would not worry about it. Just ignore her for her now. If she's not someone you're close to - let it go. She totally was out of line - yes, for sure.
I suppose in future if she approaches you (and hubby is not there), you could say something like 'You know Irene, that was a very hard day for me and our private day - to mourn our son and to prepare for his cremation/burial. It had nothing to do with you. You caused us a lot of confusion and stress. I assume you meant well but I just don't want to deal with you at this point in time. I hope you understand that. Please respect my wishes." or something along those lines.