I hate my best mate's daughter?

I have a very good friend who i enjoy socialising with. And in the past few months we have, for whatever reason, started spending alot more time together. The problem is that when she can't get a babysitter we have to organise "family" outings where she and her boyfriend and daughter accompany me, my husband, my son and my baby daughter on days out etc. This would not be a problem were it not for her daughter. I'm quite a tolerable person, but i am also a very disciplined parent. My son is very well behaved, with manners and respect for his elders. He is a very intellegent little boy who enjoys reading and constructive play. Ie, make believe games not just running riot creating havoc and chaos for no other reason than that. He has never raised his hand to another child, or adult for that matter in his entire 7 years. He is very placid and gentle. However, my friend's daughter is about as vile as you can get. And i hate the effect it has on my lovely son. I enjoy spending time with my friend but she really is a bad parent. Maybe i should give a few examples of her daughter's behaviour before you judge me as being a bad person who hates a little girl. My friend's daughter has got it into her head that she is an adult. And yes, it is her mother's fault. She demands adult portions in resteraunts. Adult soft drinks & thats just the tip of the iceberg. She has a very bitchy nature. And will often but into conversations with her opinion & has been known to tell adults to shut up. If she see's another child being told off she will gloat & think it's ok to join in with the parent! She hits my son when he doesn't comply with her wishes of "bad behaviour play" She is far too aware 4 a 7yr old & has been known to say things like "that woman over there is giving me a dirty look" what 7 yr old notices things like that??! She will demand things & when her mum (my friend) gives in, she will change her mind and in a bitchy manner say "i dont want that. im not having that. i didnt want that one!" which makes my blood boil! As time has gone on, i have found myself disciplining her infront of her mum, who sits there quite happy to let me do so! Now, this girl needs some discipline but not from me. My friend does not see whats wrong with her daughter's behaviour, and on occasion will laugh at her more disgusting actions. When her daughter makes rude comments on people's appearance, she says it's funny & will laugh. Now, i realise this makes my friend sound like the sort of person i shouldn't be friends with. But i like to think, besides that, she's a good person. Maybe i am far too quick at trying to see the good. I know that trying to do that with her daughter has got me nowhere. And now i am stuck with a choice. My son is sick and tired of her. And now my other friends, whose children have spent time with this child at my house at social gatherings, have all said they dont want their children around this girl again. Only last night my friends daughter went upto the Dad of the girl she was playing with and told him "to get away" from his own daughter!!! I feel i need to distance my son from her without causing a rift with my friend. Even my family have encountered this child's disgusting manners. A few weeks ago i was at a family meal and i bumped into my friend as they arrived. We were leaving as my baby needed to go to bed so we chatted for a moment then left, leaving the rest of my family to talk. I later found out that my friends daughter had approached my grandmother & said "oi, are you gonna come and talk to my mum or wot?" Not wanting to be rude my grandmother went to talk to my friend, who she does not know, and the child proceeded to dominate the conversation! To put it plainly, my friends daughter is a rude little ***** & i dont want her influence around my son anymore. She is a dominating little brat who thinks she is equal to adults & has the right to berate children her own age when their parents discipline then and taunt them too. Her tone of voice is downright bitchy & i cant bear to hear her speak thats how bad it has got! How do i distance my son from her without alienating my friendship with her mom? Or is that something i will have to chance because my son comes first? Any advice welcome!!!