Hi, I'd like to help you with your question.
From what you said, it sounds like you have a granddaughter who is competitive and also is having problems going to bed at night. Otherwise, your granddaughter is doing well.
Regarding her trouble sleeping, it is important that her parents or you establish a bedtime routine for her. For example, at the same time every night, have her get her bath/shower, then a snack, a bedtime story then off to bed at the same time each night. The routine will help her body realize when it's time to relax and she will begin to get used to the consistency. Children often thrive with routine since it creates a feeling of security, even if they fight against it.
There are many reasons why your granddaughter may be competitive. It could be her personality. Some children want to win and settle for nothing less. She may also feel pressure from being the oldest child and feel a natural competitiveness as a sibling. That does not mean she doesn't like her brother or feels any negative feelings towards him. It only means that she is an eldest child and they tend to be more competitive in nature.
In dealing with her competitive nature, you could let her play the party games and help her cope with not winning. Talk to her about not winning and the fact that not everyone wins all the time, no matter what. For examples, show her public figures like athletes that do not win a game and how they handle the loss, what family members do when they don't get something they want, even cartoons that emphasize not winning. Encourage her to talk about not winning and how she can make it positive by learning from it.
From what you describe, it sounds like your granddaughter is doing very well and just experiencing some normal childhood adjustments. If her home life is secure and she is well taken care of and loved, she will work these issues out on her own with support. It is good she has you to care about her.
I hope this has helped you,