The loading of a new mag could be from riding the slide forward rather than letting go, but if it is doing that when firing it sounds more like a weak recoil spring. Although it could be she is limp wristing it too. Check her stance and hold/grip and see if you can put her in a more stabile and firm position. I know many people who shoot competition are advocating the parallel thumbs 2 hand hold, but the locked thumb 2 hand hold is still a firmer hold.
The failure to lock the slide back on last round is probably a magazine issue. Does it do this with both mags or just one?