I can't stand my sister.
Why do you feel that way about her?
I find her very annoying and boring.
I can understand how you feel because I've been there, but it's only temporary and you will enjoy your life more if you try to get along with your siblings regardless of how you feel towards them.
She's not growing out of anything and she always comes to me for help with her problems. Old and unattractive.
It seems like a good thing that she feel she can talk about her problems with you but if you really hate it then you should politely suggest her friends might be more helpful in these situations.