Mana Regen bug on Illaoi

Illaoi appears to be having problems with her mana regen and I thought it was just me spending it too often or her just not having a very high mana regen. I didn't notice it until I was against another Illaoi, we were same level and yet she was recovering mana vastly quicker than I was and we weren't spamming abilities. Her masteries and runes gave no mana regen yet she had the better mana pool than I did and I don't understand if it's a bug when there's two illaoi's or a possible glitch.

The only thing note worthy is that I was landing my Test the Spirit more frequently than she was and after I did her mana regen would go up while mine went down, don't know though as she hit me with hers and mana regen was still significantly different.