Formal:
* Elle a un visage mignon. (This is the most direct translation and is suitable for most situations.)
* Elle a un visage agréable. (This is more neutral and could be used for a polite compliment.)
* Elle a un joli visage. (This is slightly more poetic and emphasizes the beauty of her face.)
Informal:
* Elle a une tête d'ange. (This means "she has an angel face" and is very affectionate.)
* Elle a une frimousse adorable. (This is a bit more playful and is used for someone you know well.)
* Elle est craquante. (This is slang and literally means "she is crunchy", but it is used to describe someone who is cute and adorable.)
Other options:
* Elle est jolie. (This means "she is pretty" and can also be used to describe someone with a cute face.)
* Elle a des traits fins. (This means "she has delicate features" and can be a more sophisticated way to describe someone with a cute face.)
The best choice will depend on the context and your relationship with the person you are talking about.