Have a daughter with a bad attitude, problem she is 34 and uses it on me.?

I have a 34 yr.old daughter, mother of 4 and she is the bossiest little brat...also she has a nasty attitude and has no problem using it on me. Question: What do I do to curb it? she knows a 23 yr. old whom she claims she has to be friends with because she is her hubby's brother's girlfriend. this girl has called me an old b.... and has really hurt my 14 yr. old granddaughter's feelings with something she and my granddau's half sister did on myspace. all this 23 yr. old has to do is say i am sorry to my dau and everything is water under the bridge...they got into a disagreement about what family really was and this b---- told my dau. to look it up...so i did..sent my dau. the def. of the word and the name of the book and the pg. no. she has a bad blog on my dau. best friend because the guy she is with is the best friend's ex..she got a e-mail with an apology and i said she apologizes like i change underwear and my dau. told me to knock it off. should i slap my dau. or ignore her?