Vexthra coming to the tower wasn't just to see her sister and spend every day having sex with her husband. She had no plans to waste time.
Her major plan was to turn her sisters into powerhouses.
She is a god, so until Kent enters the god realm or finds himself in a unique world, she won't be able to help him with anything combat-wise.
She is basically useless in that aspect, so as someone who had given him the quest to kill the God of Alchemy, she knew Kent would need all the help he could get.
This made her invest her strength in her sisters.
Unbeknownst to her, the simple human she gave this mega quest to was actually someone the universe fancied in all ways and forms.
Kent, who was meant to rise through the ranks and one day challenge the God of Alchemy, was actually badass from the start.
And this greatness now started to affect her sisters when Kent started bestowing True Names on them. She basically had her job cut in half for her.
