Here's why:
* Collective nouns are often descriptive of the group's action or purpose: Think "flock of birds," "pack of wolves," or "choir of singers." It's hard to assign a collective noun based solely on physical appearance.
* "Beautiful" is subjective: What one person finds beautiful, another may not. It's not a universally agreed upon characteristic.
Instead of trying to find a collective noun, you could use more descriptive language to evoke the beauty of the group, like:
* A bevy of beauties
* A stunning array of girls
* A radiant group of young women
* A collection of charming ladies
Ultimately, the best choice depends on the context and the specific image you want to create.