Aw gee... sometimes it feels like the only time we open our mouths is to change feet? Candy, I would begin right where you did with us... OOOO I'm doomed.. or such...and say you noticed she didn't reply and when you reread your email you couldn't believe you had said what you did... maybe add in stress and fatigue... and asking how you can make it up to her and her sons, who have been such a help etc.

Regardless of her response, I would follow up with a card of apology or if she forgives, of gratefulness. What's done is done... do what needs to be done now, and move on.