OK i can totally see why you're stressed out, is there any chance you can get a babysitter to give yourselves a break first of all? (even if you go out with the girls and dp babysits) you could do with going out with dp really to chat through how you are going to handle it all as you are both going to need to be strong and united in your approach or this will not work as quickly.
i would clear out her room, take it back to basics, def take away the stereo (do not give it her back it will make things worse, imo she is too young to need a stereo in her room anyway)
do a sticker chart, BUT YOU HAVE TO STICK WITH IT, BE CONSISTANT, give her a sticker for every 2 hours she is good (dont worry too much about wetting herself, if you can tackle the other stuff it will come together)
at the end of the week give her a treat for the stickers she has earnt (no matter how many she gets) tell her all week she will get a treat for the stickers she has earnt, when you can see she is about to go off the rails distract her and talk about the stickers and what treat she would like at the end of the week, give her little incentives as well, (i dont mean buy her stuff) i mean outings, feed the ducks if shes good etc.
either completely ignore the tantrums or give her a time out for it.
i hope some of what ive said will help.
i had trouble with a mindee a few weeks ago, he was being quite a handful with hitting, spitting, kicking, punching, being defiant etc and this is what i have done with him.
make sure bed times are calm and tell her what is coming, so after dinner say in 5mins we are going to give you a bath, 5 mins we are going to get you out of the bath, 5 mins we are going to get you dressed, 5 mins story, 5 mins cuddle and kiss then straight to sleep etc. i always say i love you and shut the door.
The running commentary is quite good actually, i use it all day so they always know whats coming.
maybe she is jelous, maybe she is finding it all new etc but it cant carry on like this can it. you are her mum and you can do this.
i really hope things improve, this will just be a phase. be kind to yourself get as much chill time as you possibly can. get dp to do bedtime for a bit and take yourself out for a drive for 15mins just to get out every night if it makes you feel better.