I. Being a bitchy person is a bad thing at a work place. So talking to such people will not work, unless they listen to us as though we are counselors. That's likely not going to happen. So, just ignore and do not react. Normally once a person like her realizes you are a hard nut to crack (i.e., if you don't show you are effected by her bitching), they will stop bothering you. It takes two hands to clap. So just move out of her destruction path if it's possible. They are not worth even worrying about.
II. If she has more powers at office than you, then it's a whole other ball game, she could effect your job position. In a worst-case-scenario, step 1: Talk to her (so she gets a warning that you may react officially)
If that fails, 2. report to your immediate supervisor....they normally as per policy must hold an official meeting with the offender and victim to talk it out.
If that fails and the supervisor does not take action (usually right to go above the supervisor, but then you have 2 people you have to go against. Hence 3. I would make good of the job while looking for other options and move on. (But I don't recommend this safe...as one needs to be cautious in todays bad days...because there are lesser permanent jobs out there in any part of the world.
III. So your best bet maybe to assert yourself and stay....get lost in your job and don't worry. It will show in your appraisal whereas the bitchy person may have to officially shut up because such things are basically born out of insecurity.