I hear ya! I get that too. I am 27 and a single mom, so I get disrespected by other parents b/c they think I dont know as much and cant do as much as they can because of my age and status - they are wrong by the way (even the teachers at my dd's DCP say that I take better care dd than most of the other parents there).
I think my approach would be somewhat childish - I would guide my dd into the DCP and simply do what she does...
"Come along, we dont want to get in anyones space today - we might get hit"
On the other hand - I think would take your approach and simply be the bigger person, this lady obviously stinks. I dont like people like that. But simply try to keep them apart for the few moments you are all together. Is there anyway you can arrive 5 minutes later to avoid possibly running into her, I know that avoiding it isnt the answer but if you really want to keep your son there, this interaction you have isnt appropriate and you certainly dont need her stress and aggrevation.
What about speaking with the DCP??? Maybe she can offer some light on this issue.... she can lead the 2 children into a seperate area immediately so that this lady's issue doesnt effect their interaction with each other? ANd you can just go about your business without saying anything to the other mother?
Good luck.