It sounds like she is bored and also looking for attention. If you don’t have one in place, I’d suggest reward charts for all of the children. Have about five things you want them to do, maybe include one specific ‘job’ for each child and then subject to getting a certain percentage each week, you give money that can be spent on sweets or some other reward. You could discuss this with the children and the rewards might be different depending on the child.
You could have set jobs around the house - simple tasks and have a price list so if they help with them they get 10, 20 or 50p. This might motivate them to help out, give them something to do and wouldn’t break the bank.
In terms of money being stolen, this would happen to me once and not again. In this age of cards, easy to live without having any cash. Keep all money/cards etc on your person or under lock and key. If anything like this were to happen again, I would explain to her that this is theft and take her to a police station for a chat with a police officer to help her understand the consequences. She needs to see that her actions have some kind of consequences, at the moment there are none.
If they can’t behave responsibly with pens, again, I’d keep these all under lock and key until such a time they can behave responsibly with them or only allow them to be used under supervision. Consequences for damage from pens would be withdrawal of a privilege which as having a guest over, not grounding which seems to be ineffective on your children as they seem to get even more bored and frustrated.
I think you did the right thing in not allowing the friend over again who misbehaved along with her. As your child is doing this on her own though too, she may be doing the leading astray. As she likes having friends over, perhaps that could be the reward each week?
In terms of throwing/damaging toy items, especially those which are expensive, I’d refuse to replace them so she has the natural consequences flowing from it. I’d also explain too if someone gets hurt from her throwing toys out of the window (this isn’t just a property damage issue, this is a hazard), that this is also an offence if she hurts someone. Frankly though, I’d lock the window to that room so it’s not an option for her to just easily toss items out of the window.
If she is generally impulsive and needs to burn off energy I’d try and build in some soft play/trampolining sessions. If you can’t afford that, I’d suggest taking them to the park several times a week during good weather so they can burn off more of that energy.
If she’s taken on the ‘leadership’ role too with the younger siblings, try and use it to your advantage, stroke her ego a bit and try and get her to help you with them. Although very hard when they’re behaving so badly, try and praise her for any good behaviour even little things like brushing her teeth, getting ready for going out on time, as she needs to be steered towards seeking attention for positive behaviour as most of the reinforcement is of the negative behaviour.
Good luck with it all. Parenting is really hard and I hate it when people criticise and say unkind things without having lived another person’s experiences or write some random waffle. You’re doing the best you can and you’re here because you’re looking for help.
I would also advise watching some parenting videos including some Super Nanny. Not all of what she does will apply here but you will pick up some ideas from seeing them in practice with other children.