I'd w have a chat with her and basically give her the choice of either you being a 'probably' but if you go very overdue or have a difficult birth, you'd have to back out, if if she preferred you to say no now, given how expensive weddings are.
I had ax planned section, and would have been fine to attend at 3w, and in hindsight, well enough within a week. But with a natural birth, you could go 2 weeks over, then be induced with a long labour, recovery eyc, so it's possible you'd only have recently got home, in which case going would be unlikely.
Equally, you could give birth a couple of weeks early and baby will be 5w.
Basically, you can hope to go, but you can't give any guarantees, so it depends on how your friend feels about that.
And before someone inevitably mentions that you'll be 'bleeding and leaking', again you may be passing big clots and soaking through lots of pads, and leaking everywhere, or you may never leak and your lochia be no worse than a period, and over already. Things vary so much.
Personally I'd give it a shot though (and have said yes to social stuff within a similar time for my next baby).