I can understand why you'd want to know what went on OP, so would I- but truthfully, bringing this up with your friend now is not going to do any good for your relationship with her.
Let's say she did say this- do you really think she'd say it for no reason?
If she would, then why?
And if you don't think she would, in what context would she?
You've also not got any "evidence" as such, so how is this conversation going to play out?
"My husband said you called him xxxx but he can't remember why, what can you tell me about it?"
If you could at least see the post then you'd have context for yourself to make a decision.
"My husband mentioned this post where you were talking about xyz. He commented abc and you called him a xxxx. Can you tell me why?"
If you then add - "It was 2 years ago." then your friend might be wondering why are you bringing this up now?
Your husband needs to take responsibility here. If his behaviour was questionable then he needs to account for it - and if it wasn't then he needs to explain why he's only bringing this up now.
And I'd be looking at your husband for more explanations and context before questioning and possibly really upsetting a friend.
You also need to consider that if you ask your friend for an honest opinion on something, you may not like the answer.
My advice would be to question your husband more. If he can give more context then great- if not, it's not an issue because you're going to see your friend anyway. I'd advise you to not bring it up and have a jolly good catch up.
If something feels off during the catch up then you reflect on it, see her sooner next time and address it all then, but only after you've seen the post your husband is referring to.
Literally, go on her profile and put in the exact wording she used into the search bar, or on your search bar put her name with that sentence in. It may bring something up... but what will you do if it does?
I wouldn't want to fall out with my friend or my husband here. Talk to your husband first. He has more information.