User blog comment:Lord Zeref Dragneel/Top 25 most powerful characters/@comment-25111584-20150812160455/@comment-1153699-20150814083542

It doesn't take long, yes, but the only time Mira actually trained hard was for the GMG (and maybe in this past year, but by the looks of things, it seems she didn't. And even if she did, I think Erza trained harder than her). And after that, she continued to be a full-time bartender.

Until now, Mira had no intention of catching up to Erza or training. And whenever Mira got stronger, Erza also did. But when Mira didn't get stronger, Erza still did. Meaning that even after Lissana came back to the guild, Erza continued to widen the gap.