Hello, everyone!
There's been a slight change in Rei's physical abilities, so I thought I'd let you all know to avoid confusion in a battle situation: she now has (or will soon have!) the ability to produce an external AT Field, which is effectively a biological shield that can
only be weakened by another AT Field (nullification) or weapons from her own world. It does appear late in canon, so this is something that could naturally, believably occur within her second body as well.
This will come into play as soon as she has a reason to physically protect Tsukasa, whom Yui's biological influence has adopted as a surrogate Shinji, from what she perceives to be mortal harm - probably as a part of the monster events, but if something happens sooner (taking on Kefka, what), it may happen then.
There are many caveats and rules, though, so she's not massive hax: you can see them
here, along with a picture of what the AT Field looks like (the Kaworu link). So if Rei blocks one of your attacks and you wonder why or how, this is why!