This is the 2709th most frequent Russian word.
васильева
"Васильева" is a Russian surname, the feminine form of "Васильев," derived from the name Василий (Vasily).
In this sentence, 'Васильева' is used as a proper noun in nominative case representing a person's surname.
Васильева купила новую книгу.
Vasilieva bought a new book.
Here, 'Васильевой' indicates possession (genitive case) of the surname, highlighting someone's new artwork.
Ты видел новые картины Васильевой?
Did you see Vasilieva's new paintings?
In this context, 'с Васильевой' uses the prepositional case to indicate companionship or partnership.