I agree that it's more about her issues that she's projecting on to you and your fiance. She's probably jealous, or has low self esteem, or who knows what. She clearly has no problem insulting people. Wow.

What she said was completely in poor taste. Joke, hardly. Anyone with any semblance of class would never say something that tasteless to a couple about to be married.

Ask yourself: is this the type of friend you want in your life? If the answer is, "no!" then just drop her from your social circle. You don't owe her an explanation either.