Anonymous wrote:For that kind of a relationship and that size of a wedding, I would agree with PPs that MIL should not have expected an invitation. However, I don't think that's necessarily a given in general. My sister is getting married this summer and my ILs are invited. But it's a larger wedding (150) and my parents have a decent relationship with my ILs. My sister knows them very well too (has been to their house for events/holidays quite a few times etc).
I agree. For an affair that small, every invitation should be for someone your sister and husband to be absolutely want to come to the wedding. My sister's wedding was large - 500 plus guests - and she invited my ILs because we all live in the same area and see each other fairly regularly, etc.