Is the word valentina the same in Brazilian and European Portuguese?

Yes

The word "valentina" is a proper noun (a female given name) and remains identical in spelling, meaning, and grammatical function in both Brazilian and Continental Portuguese. The only difference lies in pronunciation.

In Brazilian Portuguese, the vowels are typically more open and the rhythm is more melodic (syllable-timed). The "i" and the "a" are pronounced clearly. In Continental Portuguese, vowels in unstressed positions are often reduced or even "swallowed" (stress-timed). This means a Portuguese person might pronounce the "a" at the end of "Valentina" much more softly, making the word sound more clipped or shorter to a Brazilian ear.

Brazilian Portuguese Examples

1. A Valentina é minha melhor amiga. (Valentina is my best friend.)
2. Eu vi a Valentina no shopping hoje. (I saw Valentina at the mall today.)
3. A Valentina chegou atrasada para a festa. (Valentina arrived late to the party.)
4. Você conhece a Valentina? (Do you know Valentina?)
5. A Valentina estuda muito para a prova. (Valentina studies a lot for the test.)

Continental Portuguese Examples

1. A Valentina é a minha melhor amiga. (Valentina is my best friend.)
2. Eu vi a Valentina no centro comercial hoje. (I saw Valentina at the shopping center today.)
3. A Valentina chegou tarde para a festa. (Valentina arrived late to the party.)
4. Tu conheces a Valentina? (Do you know Valentina?)
5. A Valentina estuda muito para o exame. (Valentina studies a lot for the exam.)