Nina Yang is one of Penny's best friends. They met when they were teenagers and Maggie started a feminist organization. While she's obviously a feminist, Nina isn't that militant and joined more to make new friends. This extends to her LGBTQ+ activism, which is why she was very surprised to find out about the bisexual flag + manifesto in Rebellion.
Nina has a little sister, Amanda, and very supportive parents, but the Yang home isn't all sunshine and roses. Nina's grandmother never accepted her only son's marriage to a black woman and is almost as unhappy with Nina's sexual orientation, and unfortunately isn't afraid to say so. Still, Nina is pretty chill most of the times and rarely loses it. One of those rare times was when her ex, Tanya, tried to tell her exactly how wrong she was for dumping her - she wasn't, and was more than willing to explain why (Lesson One: Vampires).
Nina's aunt, Professor Wanda Gibbons turned up in Mummy Issues as the newly appointed director of the museum where the mummy was loose. That's where Amanda was seen for the first time, on a framed photograph on her aunt's desk.
Nina was a later addition to the cast which is why she only turns up in the beginning of Lesson One and near the end. That didn't prevent her from doing some vampire slaying, though. Like Maggie, she mostly turns up in scenes with Penny.