Dealing with BPD's girlfriend

[Indyan]

OK,
so long story short, after 1,5 years of supervised visitation, ex is now allowed to have S3 for the week-end and half of the holidays.
The woman he's used for harassing me right after he walked out from us when our son was 6 months old, is the one picking up my son as BPDx doesn't drive and she picks S3 after her work (1h away from my house, and then 1 more hour to her house).

Anyway, useless to say that she's been brain washed lots of crap about me (all the stuff he actually is: violent, hysterical... .).
Although I'd rather see her face than his at my door (there's always a friend of mine to open it, as BPDx, his GF and his family have used any contact in the past to write allegations against me), I feel she's getting more and more confident.

Last time she demanded that I changed S3 shoes. It was sunny, and he had leather sandals on.
I refused, saying his shoes were perfect for the weather, and closed the door.

I have now to deal with this 2 headed monster... .sometimes I wonder what I've done to deserve all this :-(

Any advice or shared experiences will help a great deal

[Turkish]

Good for you on standing up for yourself.  Who knows how long this woman will be in your son's life. 

It would be frustrating to deal with this "two-headed monster" so can you deal with her using the tools,  while not compromising your boundaries? She's part of your reality for now.

[Indyan]

Good for you on standing up for yourself.  Who knows how long this woman will be in your son's life. 

It would be frustrating to deal with this "two-headed monster" so can you deal with her using the tools,  while not compromising your boundaries? She's part of your reality for now.

Thanks Turkish :-)

News. Yesterday, it was the beginning of the first 2 day-week end for my son.
BPDgf was suddenly very very nice, and she asked if it would please me if she brought him back earlier on Sunday as it is Mother's day. She took me off guard and I spoke my heart, which I regret now. I told her that it was certainly HER idea not HIS (she denied and said naively "I swear it was OUR  idea" and also said "I trust you with my son, as I don't trust HIM, he's potentially harmful".

I realized that they're just playing nice before the meeting with a mediator in 10 days.

I'm p*ssed off with myself.

[Turkish]

I get along with my ex, and I try to be as neutral and friendly as possible.  She's even friendlier to me,  I think.  The other night she texted me asking if I had done something witch was a task for the kids that she didn't have to involve me in and could have done herself. I was so annoyed,  that I sent back a message sterner than was required. I might have even been rude.  I cool had slipped. 

Given that you are at the beginning of this,  I'd give you a break.  Keep your eyes on the prize, and if it's possible,  be friendly to the gf. She may even share information later that will be useful.  I didn't exactly play dumb,  but detached and cool.  It's hard,  especially with kids, I know.