How to deal with a mean girl?

[glittercandy]

Some girl has got it into her head that me and my friend were bitching about her on Twitter, and now she's giving us evils, calling us names etc. Today in class, all her stupid friends were like "why were you bitching about her?" and she was like "don't you just hate it when people indirect you on Twitter?" she's friends with some other tough popular girls, and I'm just worried I'm going to get bullied. I ignored them and carried on with my work, as even if I said something back, it still wouldn't be good enough and they'd be too stupid to understand. What should I do if they carry on saying things to us? It's really making me worry. Trust me, it will only make the situation worse if I have a go at her, reply back etc, so shall I just carry on ignoring them?