DS5 met her and said that she was nice. I expected her to be nice to him but it was good to actually hear it was a pleasant visit. DS5's highlight was seeing SS13's room and his different gadgets. I was happy that SS13 had this experience and his mother behaved herself as I know she is capable.
It was interesting though that DH assumed I would be upset that BM met DS and that she had given him cake so he took away the cake after they left and threw it out which caused DS to wonder what was up. My dear friend also expected me to get upset about it too but I thought it was okay. It doesn't mean that this can be a regular thing or that they could spend time there without DH but this was okay.
A couple years ago, I would have said there is no way in hell my children would ever be at that house but it happened and it wasn't a big deal. Sometimes time is the best medicine for many of these stepfamily issues.