Anonymous wrote:She didn't say it to the sister! She shouldn't have to speak to her husband with the same filter she would speak to a SIL.
This exactly. Saying it directly to the SIL would have been a problem. Saying it to her DH was just fine. DH is missing a "social cue chip" to relay that to his sister. DH owes both of them an apology.
Op, if you think apologizing to your SIL would help, you could tell her you were speaking generally, and based on the personal experiences of your friends. She's probably upset because she knows it could be true.