Mary is known for being protective of herself and her friends. It's rare to see her showing her creativity and emotions. Basically every sign that is human is titled weak for her. You could say it's hard to read her signs, but that's only because she never gave one.
Mary's addiction to The Virus started when her and Russ hung out for the first time. Russ being a scientist introduced her to a prototype of a drink that could give someone energy without any health risks. Thing is, she was the test subject. Russ didn't know what he had done till she came back begging for another glass. Mary didn't tell him what happened with her so Russ automatically thought it worked. This is also how Sam got infected too.
Mary's interest mostly consist of space. Astronomy being her favorite. Her other interests mostly consist of crafting. Her favorite being candle making. Before her addiction started she was working on Zodiac candles to give to her friends. As you can see she tries to be the father figure shes supposed to be.