I have a friend whose child used to bite at about the same age. He always seemed to bite little girls for some reason. He was slow to talk and was possibly venting his frustration. Anyway, my friend dealt with it very well, IMO. Her first step was to pick her son up and move him away from the situation, telling him that it is wrong to bite. Then, without any further fuss, she would go and console the child who'd been bitten - cuddle them, and focus all her attention on them, rather than her son. He would be ignored. Then, a little later, he would be brought to say sorry to the child he'd bitten.
I always thought her approach was really sound, as it didn't give her son any real attention for what he'd done, but did encourage him to see that it was wrong.
At 2, I think it's really hard for children to bully in the sense that we probably understand from school age (or even slightly older pre-school children). Often they are testing boundaries, or even just testing out what happens when they use their teeth in this way.
I do understand how you must be feeling (it was my daughter that this child often bit, leaving serious marks!). It's doubly difficult when it's happening within a hitherto supportive and close AN group, as often you don't want to be the one making a fuss.
I expect your friend will understand (she's probably acutely embarrassed at what's going on), especially if you explain how vulnerable you are feeling about it. Hopefully she will be open to agreeing how you will both handle any future episodes.