I think this is closer to the truth, but maybe what she resents is that Arya became who she always wanted to be...she saw her path early on and became a warrior despite everything that happened, while Sansa, the older sister, was a shallow fool that the world chewed up and spit out...
I think that she imagined Arya came home to the safety and protection of her family. She thought she would protect her younger sister, but quickly realized that it is probably going to be the other way around.
The growth of the bothers is one thing. Jon is older and Bran is still in a wheel chair so he will need her, but to have Arya, her younger sister, seemingly outgrow her, that must sting.