Multiculturalism refers to cultural diversity within a specific group. For example, you could talk about a multicultural society, a multicultural business, or a multicultural educational institution. Your question is correct to point out that multiculturalism isn't a static thing. Rather, what multiculturalism looks like can change based on the person doing the viewing. Your question asks you to apply multiculturalism to the perspective of a young adult white female from the United States.
From this perspective, multiculturalism could look like a few different things. If the person has been raised around predominantly one religious group, then being in a group with individuals from different religious backgrounds could constitute multiculturalism to that person. The same could be said if the person was brought up in a nearly all-white city and then joins a group where they get to interact with individuals from other racial backgrounds.
I think the key thing to understand here is that what you've been exposed to in the past plays an important role in determining your understanding of multiculturalism. Essentially, if you've been exposed to many different cultures from a young age, then your idea of multiculturalism may look more extreme to someone who hasn't been exposed to many different cultures in their life. The young adult white female may need to just see a few different cultures represented to feel like she's in a multicultural environment, whereas someone with a broader array of cultural experiences may need more representation to feel like they're a part of a multicultural group.