My situation was a little like yours. I have a stepdaughter Bron who's now 13.5 years old. I came onto the scene when she was six, and DH and his ex had been separated two years.

When we first met, I told her that she only had one mummy, and it wasn't me, and I wasn't going to be her mummy, I was going to be her friend. Considering that I'm only 14 years older than her, it was better to set it up this way.

We still get along great (in fact she prefers to spend time with me rather than DH!). When DS came along, she was just wonderful, and now that #2 is on it's way, she's been even better.

I try not to discipline her at all, although I do ask her to do things like have a shower or do the dishes. We have small arguments, but I don't ask her to do much, so it doesn't matter as much if she doesn't do as I ask. However, she's generally pretty good.

At the beginning, I didn't discipline her or comment on her behaviour at all. I think it would be very different in your situation because your DH has obviously been around longer than I was at that stage, and there's probably a greater age gap than 14 years! Bron's half-sister is the same age as my sister! (21!) so there's some "closeness" there too.

Hope my comments help (although I don't think they really will because of the differences in your situation and mine!) Getting Matilda some counselling is a marvellous idea, kids often open up so much when talking to a professional, it's just fantastic.

Best wishes.