Well, did they really 'pound' on the door? If it was a bad time, you should have let the know right away, but you let them in regardless....so, that's kind of on you. It sounds like you don't like this woman, and while I don't find what you said rude at all, she took it that way probably sensing how you feel about her...
REGARDLESS, you are the one with the baby and people need to respect that...if she can't call before stopping by, I would not even answer the door. You are busy, and you have a two year old, and your husband needs to understand that you are not an entertainer...I find that people get very 'friendly' when there's a new baby involved...they always want to come over, have you stop by and if you don't let them 'see' the baby, hard feelings develop...my feelings? I don't fukking care.
I'd explain to your husband that SHE needs to get over it...and if she milks it, I would not even entertain it for one second. If she mentions it again, say, "I was x amount of weeks post partum and my hormones were going crazy. Thankfully, it's in the past and I know you won't hold on to it because you're not petty like that..." If she mentions it again or argues, simply say, "I'm done discussing the issue."