Is this girl my friend or just a b**ch?

okay so this girl and I are best friends. when we hang out we have a blast and its great, and we always have so much fun, but its so weird. my parents constantly fighting and stuff and apparently I have issues with standing up for myself and stuff, and she's been helping me with that. then when I do something wrong, (I sometimes don't pick up my phone when I'm busy and stuff.) she leaves me these nasty voice messages on my phone and I don't know what to do. then we get into these fricken huge fights and she's like, "yeah, well who gave you a shoulder when your family didn't?" which is true, and idk its just bad brining my family into these things. anyway the next day things are usually ok, but she's always asking me to do mean stuff and she's pretty mean when she's mad. should I break off the friendship? I'm so tired of all this dramatic crap, and yeah we have good times together, but is it really worth it? its just so screwy. what do you think I should do? thanks in advance