Re: Old fashioned father...
First of all, I am so sorry your neice isn't able to tell her mom, the one person she should be able to talk to, but I am so, SO happy that you are there for her to talk to about important things. It's extremely important for all young girls to have a positive female role model. I'm sure she appreciates you being there for her.
Having said that, I can totally understand her not wanting to tell her dad. I was 11 when I started my period and wouldn't tell my dad because it was too embarassing for me. I told my mom and then didn't even think twice about whether my dad would or wouldn't find out.
Unfortunately, regardless of how "old fashioned" her dad is, he has to face the fact that little girls grow up and their bodies change. It's a normal part of life and a normal part of being female. I would hope her dad wouldn't make a huge deal of this because this isn't something she can control. She probably wishes it hadn't started herself! I know my daughter thought it was disgusting when she first got her period.
I think you should ask your neice if she is more comfortable with you telling him about this. After all, if her mom isn't around and her dad is responsible for raising her, he is going to be the one who has to purchase her feminine products since she can't get them for herself. He has to know, and if he needs help in dealing with this, and her mom isn't available, then maybe you will have to help him come to terms with it. You can also offer suggestions about which products your neice will need or prefer and you will also need to make him very aware that this in no way is a bad thing and he needs to not make her self conscious about it.
She is growing up, and he has to accept it. Take care- you are a good aunt.