I have two step kids (8yo daughter and 9yo son).

My DSS is a great kid and although he has a temper he is learning how to control it. My DSD on the other hand has an attitude which has been getting progressively worse over the last 6 months and she has also started throwing tantrums for what seems like no real reason at all.

We have noticed things have gotten worse since we discovered that DH and I are expecting a bub in Nov, so have for the most part rationalised her behaviour as trying to work out where DSD will fit into the family unit when bubs arrives but I also don't think we should accept this behaviour and have her think that it is ok.

The most recent tantrum was yesterday - after having a morning of her refusing to do anything I asked (and for the most part wasn't a big deal that I let slide) but in the afternoon I asked her to clean something in her room - I asked her politely in which I got a responses of 'ah no' accompanied with an attitude filled smirks. DH then pleaded with her to do what I asked and after asking multiple times from either myself or DH I told her that if she wasn't going to clean it that I wasn't having it in my house and took the item to the garage. This sparked the tantrum. (I'd like to note that neither DH or I raised our voices or yelled at her during this whole situation) DH had a go at me for it (whole other issue - where DH undermines my authority but that's for another thread) and grabbed the item - I then decided that he could manage the situation and after a lot of yelling and crying (all DSD), DH managed to get the item cleaned - it took at least half an hour. This was the third tantrum in a week.

DH doesn't have a good relationship with his ex so can't speak to her about DSD's behaviour but DSS has told us the DSD does behave the same when with her.

I was wondering if anyone has been through this before and how did you manage it? I would like to try to do something to address not only the tantrums but also her attitude.