I think this has been discussed before, but I can't remember what the Etiquette mavens said.
So here's my deal: My friend from high school has two kids. She and her husband and their two kids are planning to come to the wedding. When I saw her at the bridal shower last weekend, she mentioned that her mother was planning to come along for the wedding weekend and watch the kids. Her mom was just planning to come along so she can watch the kids in the evening (my friend's plan).
We have had a number of declines and our guest list is looking really good. So I'm considering inviting her mother to come to the ceremony/reception. Is this considered b-listing? I don't want to be rude, I just want her mom to enjoy herself before she watches the kids and I think she might enjoy seeing the ceremony and having dinner. She will probably also know some of my Mom's friends.
Tl;dr: Is adding a guest for my friend after the RSVP deadline considered rude?