ExH has a new partner, need a handhold

[tobeornottobethatisthequestion]

My exh and I split 3 years ago, he left... Relationship was strained for the first year but we've become very amicable for the sake of our dd. We still spend time together as a family, holidays etc.
I knew the day would come, but it's hit me like a ton of bricks. Everything's going to change again. Any positive experiences to share?
His new partner has 2 dc, 1 similar in age to ours. I'm not sure when to tell our dd, or how long until she should meet them all. They've been dating around 6 months, but it sounds like they're serious, so this is a big deal.

I think you both need to sit down and tell her.
Decide together, what you are going to say to her.
It's hard.
But you will get through it and your DD will be fine.

It’s a big change initially but this may well turn out to be a really good thing. Maybe now you can really start focusing on yourself.

Maybe he should introduce new gf as his friend and let your dd get to know her a little first.

You dont need to tell her anything. It doesnt need to be a huge converstation. He needs to. He should just introduce as a friend then go from there, ideally.

If they have been dating 6 months, anytime onwards is a good time to meet.

But you need to let him deal with this.

Thank you for your advice.
I agree it has to come from him, but we thought that if I was there too, she could see that I'm not upset (even though I am) and ask any questions. It will be more casual than I'm making it sound though.