[quote=Savo]
I feel so confused after reading her back story xD
[/quote]

Well, she is telling her story to someone else. So we are seeing it through her memory and eyes. Basically, she grew up in a home with her father and his second wife, her step-mother. Her birth mother died giving birth to her. 

For a reason unbeknownst to Ryuko, her father divorced his wife and ran off to be with Ryuko's best friend, whom had just turned 16. Ryuko comforted her stepmother and life continued on. Some time later, Ryuko found out that her stepmother had either begun to or had been prostituting herself to make ends meet. Ryuko beat the crap out of the John. To keep their silence about both the prostitution amd the severe beating, the John pays them monthly checks. To keep her from getting a criminal record, her stepmother and the John lied about the incident and neither brought up charges against the other. After that, both women got jobs to pay the bills and so her stepmother wouldn't feel so alone. 

More time passes and it is Nationals. Ryuko helps her team win the trophy. That night, she has a sexual encounter with her stepmother. That blossoms into a nine month sexual relationship until both decide that it isn't healthy for the other. Her stepmother meets someone a few weeks before Ryuko is kidnapped. At that point, Ryuko threatens the man to take care of her stepmother and to treat her as a queen. The man agreed that her stepmother and the two began to date. The day before Ryuko is kidnapped, the couple announces that they are engaged and will be married in a year. 

Now she wants to get back so she can walk her stepmother down the aisle and pretend that it is her that is marrying the woman. She knows that it will never happen, and she is honestly happy for them both. The end of it is basically her amused reaction to the listener's (not us) disgust at the pedophiliac, semi-incestuous nature of the relationship, and she remarks that she never claimed that she was normal. Only sane.