When was the first time someone besides you or SO put the baby down to sleep, either at bedtime or a nap?

I'm a SAHM, and we've never had a babysitter yet, so C has never gone to sleep for anyone besides me or DH. Last week MIL was watching her while I got my haircut, and C was happy, took a bottle no problem, but when she got tired and MIL tried to put her down for a nap (following my exact nap routine, except she did the sleep sack wrong) C freaked out and wouldn't calm down until we got home shortly after. To be fair, it was only our second day there, she wasn't used to MIL, it was a new room for sleeping, so I can't blame her.

But I'm wondering how to get her used to other people putting her down, as eventually, we will want to go out when she will need to go to sleep. I'm thinking we will have BIL come over and put her down for a nap or bed, so she is at home, with someone she knows but isn't me or DH.