* Abstract nouns represent qualities, concepts, or ideas, not concrete things. "Friendly girl" describes a person, which is concrete.
* You could use abstract nouns related to friendliness:
* Friendliness itself is a good option.
* Kindness, amiability, cordiality, or hospitality could also work depending on the specific context.
* You could use a more general abstract noun about people:
* Companionship, affection, warmth
* You could use a phrase to capture the abstract idea:
* The spirit of friendship, the joy of connection, the warmth of a welcoming heart
The best choice will depend on what you're trying to express.