Well, the thing to do is leave the tags on (if they have them) and haul that stuff back to Babies-R-Us, Target, Walmart, etc. and return as possible.
With first babies it can be a real boon to have a shower and get things you need - because it can be overwhelming. Traditionally, showers are not given after the first baby. (But you know how that goes - plenty of people out there having showers for #3 and onward). IME, the books also recommend as huge excess beyond what you actually need. You just don't know until you actually have the baby in your hands and have to figure out your own routine and how to deal with the day-to-day. Some babies like swings, some hate them, some babies like excersaucers, some hate them, some babies need 2 months worth of newborn sized clothes, other need 6mo. sized clothes from day one.
Presumably none of the guests got together and planned to give multiple outfits. I think outfits become a sort of "add on" gift when you bought a baby bathtub or a diaper genie or whatever. Like, the clothes are much cuter. If she can't return them then she can either try to sell them on ebay or craigslist as a wholesale lot/bundle or she can donate them to a women's shelter.
A 529 would be great, of course - but considered crass to ask for "cash" in the place of gifts *shrugs* - she can start a 529 with whatever she gets from returns. I opened my son's first account when he was about 1 month old!