This is the 17773rd most frequent Russian word.
улыбнулась
"Smiled" (past tense of "smile").
In this sentence, 'улыбнулась' is used to indicate a simple past tense action showing expression of happiness.
Она улыбнулась, увидев подарок.
She smiled upon seeing the gift.
Here, 'улыбнулась' conveys the reaction to hearing something amusing.
Когда я рассказал шутку, она улыбнулась.
When I told a joke, she smiled.
In this example, 'улыбнулась' highlights a smile given as a social gesture or out of courtesy.