And that's way back in volume 1 when she did not know anything about Ki. She's much stronger now.
Though I don't remember anything concerning her durability.
For the fight, I think that Sando has the upper hand. Her only difficulty will be to get past the Herculean Armor, but I don't see Erza landing a hit. So either Sando wins, or tie.
Hm, this isn't a bad matchup imo but I give Sando the edge in destruction power and in reaction speed. Erza's various weapons and armors help her balance the fight somewhat though, even with Hapki blasts, I could see her Herculean Armor tank at least one or two. But overall I'd have to give it to Sando, she will outlast Erza as she is now.