if you're melee, constantly circle-strafe and doge her attacks. wait until she starts spewing lava, then run in and smack her. you can also hit her legs to damage her.
basically, continuously do this 'til she's dead. make sure you don't trap yourself in lava either. try and keep it contained.
when she crouches down, run away. she's going to to an AoE roar. --- "Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." - Albert Einstein LoL IGN: nvmvoidrays
Wait until it rears to spew lava, move around to its side, hack it a few times and be ready to run away if it's going to do the explosion thing. That's...it. This is actually one of the easier bosses. I don't say that to be mean, but man you're going to have a rough road ahead.