Question mostly for girls, but guys answer if you can help, need advice please?

i am a 20 year old guy, and my little sister is nearly 10, when she was growing up her dad was never there, and i pretty much was her dad, even though mum was there always, if felt like that father figure and have always felt an incredible amount of love for her and would die for her in a second, we have always been very close but lately she doesnt talk to me and just swears at me and says she hates me and stuff like that, i know she has been getting picked on at school by one girl cos she is pretty small, but would this make her act like this towards me, and should i be not as close to her and leave her alone and back off, or just keep trying, it really sucks cos i love her but she treats me like s**t, any advice please, is this just normal for a growing girl or what?Question mostly for girls, but guys answer if you can help, need advice please?
Its her age, When I was 12 years old I use to be really crancky and bitchy with my mom not that I still aint cause I Do get my moments still with her, your sisters hormones are probally changing and maybe it is because of school maybe try to take her out somewere to try to let go of some of her stress and maybe to try to have a conversation with her and let her know that you are always there 4 her and just talk to her. well good luck with everything. and I agree with the woman above me. Dont let her push you away be with her thru even the hardest situations and its a cry 4 help. well good luck and I hope everything works out.Question mostly for girls, but guys answer if you can help, need advice please?
Since you are 20 pay a visit to her school and speak with


the principal. Ask if your sister is doing okay and let the


principal know about the bullying. Something is wrong and


her change in behavior is a cry for help. Don't let her push you away. She needs you.