In "Closing Time",yes we saw river in the suit but in the wedding of River Song somthing might have changed like river getting out of the suit and the eye patch lady in so all kind of things could happen.
How about "because this is a show about time travel, therefore two people can be in the same place at once, Blinovitch Limitation Effect notwithstanding"?
I'm gonna go out on a limb here and say that, if that was indeed River Song, it was a version of herself in a different timeline, probably a future one, as the River Song who was invited didn't seem to know who the Astronaut was whereas the future Doctor did.
The eyepatch lady was quite clear that they were fiddling with her memory (even more than the Silence normally do) so it might have been a past or future version of her (and the version in the astronaut suit looked more desperate to find him, kinda younger, than the version at the picnic, who was experienced enough to go "of course not" when her gun didn't stop the astronaut)
The "Of course not" might have related to River's realisation that an earlier instance of herself was in the suit but it might simply have meant that she'd remembered that NASA spacesuits were designed to stop micrometeoroids (which have more kinetic energy than pistol bullets) and were effectively bulletproof -- covered in kevlar, except for the faceplate. If the Silence had only wanted something to keep the wearer alive underwater, they could have used a diving suit. Using a spacesuit suggests they had something more than that in mind and the kevlar covering of a spacesuit may have been part of that something more.
Also, in River's timeline, it wasn't "at the same time" -- it was only "at the same time" according to the calendar, which doesn't mean much if time travel is involved.