This is the 9475th most frequent Polish word.
wesoła
"Happy" or "cheerful" (feminine form).
Here, 'wesoła' is used as an adjective describing Ewa, indicating her cheerful mood or personality.
Ewa jest bardzo wesoła.
Ewa is very cheerful.
In this sentence, 'wesołej' appears in the feminine locative singular form, describing the 'atmosfera' (atmosphere).
Dzieci bawiły się w wesołej atmosferze.
The children played in a cheerful atmosphere.
Here, 'wesoła' is an adjective that agrees with the feminine noun 'piosenka' (song), conveying a sense of liveliness and happiness expressed through the music.