I read an interesting theory that Kagura sent her to spy on Mystogon (Jellal), but I guess we'll have to wait and see.
I would like to see this theory in full because, if this were true, that would be some ridiculously amazing foresight that Kagura possesses. That's saying that she would suspect Erza of still having ties to Jellal despite him busting out of prison during the 7 years she wasn't existing. Actually, it would be more believable if Kagura was keeping tabs on Erza if Milliana told her of Erza and Jellal's relationship. But if that theory really hinges on Kagura suspecting Mystogan of being Jellal, that would be the least believable situation. I would honestly wonder how she would have made that connection.
I would honestly wonder how she would have made that connection.
Well, the fact that Mystogan disappeared some time before the 7 years that FT vanished and that Jellal (as Mystogan) was stopped half way doing his distinctive spell, could have been enough for a person that lives her life to kill (and thus to gather all possible information about) certain person.
A real Colossal Sword, is only Colossal when it is at least 5 times bigger than the thing you pilot: