Mental health and tantrums in 5 year old

Hi to the lovely community here sorry for the long post. I have 3 children (2,5&6) my middle child (daughter) has always been what I would call highly emotional. Even before becoming middle child (everyone keeps blaming our issue on being middle child) but I wanted to ask here as I thought there would be more people experiencing this with children no matter where they are in the order of things.
Our issue is that she is highly emotional. She can be quite negative from the moment she wakes up. Her brother just talking sometimes annoys her and she just loses her sh*t basically. she will lash out (snatching things from her siblings, telling me not to talk to her as she storms off to her room, she will scream, try and slam her door, yell out from her room, throw things, she stepped on her younger sisters sunglasses once and broke them so I made her replace them with her pocket money that she had earnt. I explained to her that even when you get angry, frustrate or upset, breaking something of yours or someone elses isn't right and she needs to replace them with her own money as they were broken from her actions. So she got upset about it but understood and we went shopping a week or 2 later to buy them and she even told the shop assistant why she was buying them and who for. I used to discipline all kids the same and yes on the occasion would get a smack on their bum with the wooden spoon. Not hard, never left a mark, but most of the time just getting the wooden spoon was enough for them to understand what they have been doing is not right.
I have since changed my direction with her as nothing was working. (time out, spanking, where as with my son, time out and the occasional spanking worked and he now is a very disciplined child but he is much quieter than his sister).With my daughter, I can usually catch her before she loses her mind as I can see a trigger at the time or I know she is tired and the things that annoy her. So before she completely loses I send her to her room - not because she is naughty but just to calm down (she knows this and is told this each time she is sent to her 'quiet space') I finish what im doing quickly and go in and talk to her. this tends to work a lot of the time. If she gets really upset I'll send her to her room and do the same (go and talk to her). But I just feel like its getting worse. She is now talking back, if we take something from her that isn't hers, she says to us, meh, ill just go and get it anyway. I'm much more patient with her than I used to be and try and explain that even if she is tired she needs to still listen and treat others nicely. But its just getting worse. My husband has no patience for her and thinks there's something wrong with her. She definitely needs more attention than the other 2, I try and give her as much as I can with out the other 2. I don't know if this behaviour is normal for a child of this age or if she has anxiety or what not. She screams so loud and now my 2 year old is starting to pick up the same behaviours. but she is even more stubborn than her sister. Has anyone got any other coping skills or things that I can do to help my children. I hate smacking. I was smacked as a child and don't hold anything against my parents. but I really want to try and deal with this without spanking. as I just feel bloody terrible. and I dont want her to feel picked on as she would generally be the only one now who would get a smack :( I dont know what else to ask here but can anyone help with ideas. please dont crucify me for the spanking too please.