Valentine keeping peter under control
Valentine would probably be the only thing that keeps peter calm. Peter wanted to play buggers and astronauts with ender and this game can get pretty cruel in may ways. Valentine would have talk with him and rationalize to keep him from seriously hurting ender.
Helping Enders Depression
Valentine And Ender's relationship
valentine helps Ender by letting him know that there is someone out there that actually loves him and still remembers him. She keeps him save when he is around peter and tries her best to protect him.
Valentine when Ender goes to battle school
Valentine was emotional to start with but got use to the idea that ender was gone. She kept Writing him letters but he never got them because of Graff. Years passed and she was about the only one that still remembered him and celebrated his birthday.