How do i gain my confidence back?

ok so i have this cuzin nd she can b very nice nd fun and sweet-but sumtimez itz like she haz thiz alter-ego nd she just makez me feel like i am da ugliest person in da world!! she haz a size D in ba nd i hav a size C im in 7th grade, nd she uzes her az he main souce of confedience and a way 2 put me down and evey time i go 2 her houz nd we r bout 2 go sumwer she hogz up all da hair stuff nd i end up looking like i just woke up, i used 2 hav LOTZ nd LOTZ of confedence but now i barley have any itz causing me 2 think about being emo i hav cut myself be4 but not vey often how do i gain my confedence bak and feel y again