I have a really simple rule - if you and your children come to my home, they follow my rules. If you don't parent them, I will.
It works well, and all my friends with kids are well aware that their children cannot disrespect our home and our property. TBH I think there are a few parents that like it this way, as often the children will pull up quicker and better for another mum than they will for their own.
Having said that, there are obviously somethings you just cannot control, and sometimes that includes your child's behaviour - something you will find out, probably to your dismay, as your boy gets older! LOL
But I would probably speak with her, and let her know you are not happy with the way they behave in your home and ask her to step in sooner to calm the situation.