I'm sorry this is happening.. I am not familiar with your story - Sorry- but She sat 2 houses down and let SS walk to your doorstep? How old is he? I'm assuming, but I'm sure your SS is welcome in your home anytime, but I sure understand about not wanting BM around for sure.

I would have DH talk to bm and let her know that it is appropriate for her to call in advance of a visit and because of the confrontation, he needs to be there always...

Stepwitch
Thank you Disney for portraying a positive image on all stepmothers!!!!

The bm in my situation has made it so I hate her guts. I came into it with an open mind and a complete belief that if I give respect I would get it...I was wrong. The bm has barged into my home repeatedly over the months and really pissed me off. She has no manners and no respect for boundaries. Her whole m.o. seems to be "I don't want him, I cheated and left him, but nobody will have peace with him..." I completely hate and despise this woman, even though I'm supposed to be all nice and new-age and all...she just makes my blood boil.
So I can completely relate to your situation. Here's what I would do...actually I got the advice from a wonderful person on here and it worked so well I thought I'd offer it to you...sit down with your hubby and say very matter of factly, "I do not want that woman in my home again...she is not to come here unless she calls first...and if she does come, she will remain outside until/if invited in..." plus whatever else you want to happen. And say it all very plain and matter of factly. Then, tell hubby that he is to relay these rules to bm...and she will follow them or you will take whatever steps necessary to enforce them (be kinda vague here)...but do say that if she comes into your home you will call the police and have her charged with trespassing. Say it like you mean it.
I did this with my dh and everything is under control now. He knows I mean business. I said it in a way he'd understand...much better than when I scream, whine or cry. He got my point...I'm not getting f'd with anymore and I will call the police to make my point. For me, this has really worked like a charm. BM is much more compliant, and dh takes the initiative to drop off skids instead of risking bm coming over. We've talked more now and now that things are under control, I've said that we can have bm bring over skids since she seems to have gotten herself to adapt to the new rules...and I will be enforcing them even if I have to call the police when she screws up. No more playing nice...I'm tired of trying to please everyone and be liked and be "nice"...I'm going to set up and maintain the much needed boundaries. And I know you can do the same.
Don't let anyone tell you you can or can't come to drop offs/pickups...you are a co-parent whether bm likes it or not. She has no say in anything...nobody died and made her Elvis.LOL Her power is pretty much nothing. She just is trying to control you...don't let her. I'd be damned if anyone--anyone--tried to tell me not to be in my own car for a pickup/drop off...oh hell no! She sounds like she's just grasping for ways to have control over you...don't let her.
Also, since the bm in your case has tried to assault you, document everything. Do not be afraid to get the police involved at any point...you are in charge of your home and your life, not bm.
Hugs to you,
Lil