Here's why:
* "Girlish" is already an adjective. It describes something as having characteristics typically associated with girls.
* Suffixes are often used to change the word's part of speech. For example, adding "-ness" to "girlish" would create "girlishness," which is a noun describing the quality of being girlish.
If you're looking for words related to "girlish," you could consider:
* Nouns: girlishness, girlhood, femininity
* Adverbs: girlishly, coquettishly
* Other adjectives: youthful, playful, innocent
Example:
Instead of using a suffix, you could say something like:
* "She had a girlish laugh."
* "Her dress was a vibrant pink, which seemed girlishly charming."