How awful, if he is autistic then he was obviously completely overwhelmed, he was just masking all day at school and then it became too much at home and he lashed out. Hitting a disabled child is absolutely vile please don't listen to this sort of nonsense OP.
OP does your dd have her own room (just asking because you say you have other kids) I have one with ASD and I would say this is absolutely vital for his well being. She needs somewhere she can be alone, feel safe and decompress. If she doesn't currently have her own room I would do whatever you need to do to make this happen.
The next thing I would suggest would be a daily routine for her, all written out and followed as closely as possible every day. Part of the reason she copes so much better at school is because there is a routine everyday and so she knows what to expect. If you can put in a routine for her with meals, getting dressed etc, time playing games/doing something with you, going for a walk, watching tv, doing a craft activity/building lego, reading her a story or whatever else she does to fill the day then I bet her behaviour will improve. It will be really important to stick to the routine though and if something has to change then give her lots of warning. Let her have as much time alone in her room as she likes though, if this is something that she wants/needs.
What do you do when she mocks you OP? Are you sure she definitely is mocking you first? Repeating back what's been said might help her with processing it. If you're sure she's mocking then a simple 'it's rude to mock people please don't do it' will be enough. Leave it at that and repeat in calmly every time she does it. Do not escalate it into anything else. If she tells you she hates you or whatever then just tell her you love her no matter what.
If she won't do anything she's told it might be that she has a PDA profile, this means that anything you ask her to do feels like a ton of pressure coming down on her and is just too much. It's extremely hard work. Make everything a choice as much as you possibly can. Avoid telling her what she has to do - if her room is a mess then let her have her room as mess - it probably all makes sense to her. If she doesn't want to get dressed in the holidays then don't make her - pick your battles with a lot of thought. Don't bother with consequences if they don't work, just calmly tell her that her behaviour is unacceptable and walk away.
Think about why she is doing what she is doing. Why wasn't she eating the food? Was she not hungry? Did she not like the food? Is she bored? Was she just trying to get your attention? I would have everyone sit down together and eat, she's much more likely to eat properly is meal times are part of a routine where everyone sits down and eats together - 'fussy' eating is also extremely common with ASD because children often can't cope with certain textures or tastes.
If she is doing something that you don't want her to do ie throwing food around and you know her response to you is going to be violent then just don't challenge her. The food is already thrown, it will already need to be cleaned up, there is no point putting yourself at risk of getting hurt too. I would try a 'what's wrong' approach. Ask her calmly why she is throwing the food - there must be some reason for it. Then deal with the reason. If it's because it's fun or because she wants to or some other 'silly' reason then suggest you and her do something fun together instead - just as soon as you've cleared up the mess together. The more of your time you give her OP, the more of your time she will want and the better she will behave to get your time and attention. Work out what she loves doing and use that to your advantage.
Make things fun for her OP and reward her with your time and attention. She desperately wants and needs it I promise you. But you will need to put in lots of effort to do it and make it work and it's not easy when you're juggling other kids too - it will pay off though. The last thing I'd suggest is noticing every single time she does something good. She sits and eats nicely - notice it and praise it. She plays with something nicely for five minutes, notice it and praise it (if you don't want to interrupt her behaving nicely then comment on it later). Look for the good all the time.
It's exhausting having an autistic child OP but I absolutely promise you that the more time and effort you put into making things work for her the better it will be for you all. She loves you and relies on you so much Op because you're her mum.
Good luck!