It's been 4 months now since Celaine left Maria to go train on her own and the latter has made tremendous gains over the last year.
First of all, her cultivation was able to advance from the Mid-Xiantian Stage to the Late-Xiantian Stage of the Foundation Realm. It may seem like this is fairly slow progress since it took her over a year to reach this point, but remember that Maria needs much more Qi compared to others to breakthrough because of how strong her Foundation is. Her body can hold several times more Qi than a normal person and therefore she needs several times more Qi to advance.
Considering that, 1 year actually isn't that long since even the average person from Lunar Fox City or the Battle Maiden Sect would possibly need years just to advance 1 Minor Realm.
