Ever since their simultaneous birth, Minerva had been sticking to Draco by the hip, with the exception of his time in Hogwarts at a young age, while she went to a 'Pure-Blood' School for Girls up in London for most of her youth. However, even though she was an extremely talented student, her parents decided that the longer she was away, the more distant she might become from her true purpose: becoming a Death-Eater; so she had to drop out at thirteen, and be homeschooled by Narcissa, until this day. 

After learning that she and Draco were to be chosen by the Dark Lord, Minerva had to admit that she slightly hesitated to agree. However, the safety of her family became involved, and at that point, there had to be a time where she had to choose: Stick to the plan, and let her family be spared, or hang them by a thread in the wrath of Lord Voldemort. She heard of the many things that the dark entity has inflicted, and the pain of receiving the Mark left her unsettled. 

She wondered if recieving it made her become a burden to the world, or if signified her as someone to despise or fear. This didn't mean she didn't disrespect her family's choices; she just couldn't agree that there couldn't be any Muggles. They're people, not traitors; humans, basically. It's just pure terrorism that these Death-Eaters perform. The worst part, is what does it matter whether they live in a world that plays as home for all blood statuses, and erraticate them?

Holding her twin brother's hand, Minerva kept herself somewhat composed, as she proceeded the downtown of Hogsmead. These thoughts played as flashbacks, and they only became more clear the closer they reached their destination: Borgen and Burks. She didn't notice they were being followed, but the contact of Draco's hand kept her focused. Like the naturality of twins, he and Minerva were instinctively close, emotionally and, unknown to everybody else, quite physically; though in Draco's case, compulsively. Having to be extremely protective of his sister, it was no surprise to Minerva and, truthfully, she didn't refuse. 

As far as their parents are concerned, they've only seen the pair hold hands, but when they turned sixteen, the rest was confidential. Suspicions were clear, but the twins were extremely careful in hiding it, as much as they are in hiding their Marks. In other words, Lucius and Narcissa knew nothing.