Trixie has the love of Starlight Glimmer but after an unexpected encounter one night, Starlight isn't the only one to love Trixie. Because of this, Starlight's desires change as well.
Starlight nodded and they began to get her ready to model dresses. While Starlight could see where Rarity was coming from regarding her spell, she would never admit that if the situation warranted it, she would use her spell and have no regrets.
You won't do that unless pushed too far.