I actually think YES! Paige can be Uber A, and below will be my reasons.
(First I'd like to say I actually think my number one suspect of Uber A is actually one of the liars, but I'll save that for another time. This is only about why I think this is Paige. It doesn't mean I'm actually right).
1. She TRIED TO DROWN EMILY!! Why would you try drowning someone, then just fall in love with them? Sketchy? I think YES!! That's like a woman falling in love with her kidnapper/person who tortures you. Doesn't happen!
2. Sure she also received -A messages. But as quickly as they came they ended. Maybe...