She could have stopped the entire argument by telling him that the mana training would multiply his current abilities.
"If you can lift 100 pounds, then with mana strengthening you can lift 300" for example. Just tell the meathead that imporoving his mana efficiency can make him more of a meathead.
dang, so much explanation in this chapter, wonder what's the full reason why she doesn't want anything to do with her "friends", unless she really meant that they weren't really her friends.