Dealing with the ex

I am hopping mad right now!  I just had a run in with the ex.  Words were exchanged and I could just scream!  Here's the story:

My DH decided that the kids could walk to school on their own (they are 7,9 and we live 5 houses from the school).  I generally meet the BM at school so I wrote a quick email stating that I would drop the youngest to her at her home (we have shared custody but she baby-sits them for the day when DH is working since she refuses to get a job).  I hear nothing from her my DH hears nothing from her and then this morning there is a nasty email- sent to me only- saying she does not agree with the girls walking and that she will be at my door at 8:00 in the morning.  I responded that I would take the kids to school until she had a chance to talk to their Father. 

So she shows up at the door all pissy and I tell the kids to go upstair and we have words.  I tell her she needs to discuss things with the children's Father, NOT ME.  Things digress from there.  She tells me I don't repsect her (and to be honest I really do not...I do respect that she is their Mother and they love her but I do not respect her as a person AT ALL!).  I tell her she treats me like shit.  I tell her I do not want to deal with her at all and she tells me GOOD!  She says I over step my boundries (pls note she thinks my being good to the kids is over stepping and that I am not in a parenting role).  She tells me shared custody has been bad for the kids and I tell her it has been wonderful for the kids.  She goes on to say that I bad mouth her to the kids...this is NOT true.  When we do talk about her if the kids are in the house we speak in French (the kids can't understand or speak the language) and we use a "code" name for her not her real name.  I tell her not to come to my home uninvited that neither my DH nor I show up at her door uninvited and that she should not come to ours, it is inappropriate. 

I wish I never had to deal with that heinous bitch!  I know she wishes the same and I am sure with the same sentiment. 

I have tried and tried and tried some more...I generally try to get along but today I just lost it AGAIN! 

So my question is this...how do I turn the corner (AGAIN) from absolutely HATING this woman to being able to stomach her in the least?  And do I even bother to try?