Children go through phases of gender-role identity adoption. It would be best to avoid arguing with her over gender issues. It is evident that she is identifying with her father and therefore wants to think of herself as a boy. She is declaring this identification, and perhaps showing rebellion towards you. As she grows older, you can expect a change. Peer pressure and identification with same-sex parent would occur. Meanwhile, since you do not have gender bias, it may be possible to refrain from expecting 'girlish' behaviour for some time and not referring to her as a girl. Try not to make it a power issue or take it as a personal insult. Exposure to appropriate gender stereotypes, family discussion and debate over gender issues when she is older, and her own need for peer conformity would gradually prove useful in helping her decide for herself.