I had my daughter on the Wednesday...I had a mild epidural and one tiny tear that barely required a stitch....by the following Wednesday I was downtown visiting my work and my DH work with the baby....I nursed so....I was still adjusting and my boobs were pretty freakin' sore. Hahaa. But otherwise I felt great. The worst day for me by far was the 2nd day after birth. When my uterus started contracting...I was in SO much pain!!! But as soon as that was over (only took a day or two) I felt completely normal. My stomach had gone down tons as well....a wedding seems pretty adventurous Hahaaha. If you had the luxury to, as you said, pop over...visit...hang out and then go relax when you felt like I'd say go for it for sure!! Most places usually give final numbers just a few days before so I'd tell your SIL you want to go and ask what her cut off date is? You could even go early and have even longer to recover...who knows. Chances are you won't but at least find out what her cut off is so you know when you have a final say. One person won't make that big a difference....good luck though