I have a son with autism, and it makes me mad to think that the seriousness of your daughter's experience could be in some way diluted, due to his lack of understanding.
His going to the trouble of inventing a 'reason' for doing what he did (i.e. swallowing a stone), is a bit suspicious. Mostly because most kids with autistic spectrum don't 'do' secrets very well (never in my case), so I am surprised/suspicious of what exactly was going on?
We do struggle with appropriate behaviour at time. Rules have to be carved in stone, and consistently reinforced behaviours from everyone (long term effort, hopefully it will pay off).
My view on ye moving house - I wouldn't. It is your daughter's home, why should she have to move, particularly if ye are all well settled, etc.
My experience has been that once a behaviour has been identified, then usually work can be done (if parents, etc. are willing) and the world around you becomes better/safer.
As an abuse survivor, I feel that others underestimate how resilient children can be. If they are happy and secure in general, then I feel that abusive behaviour, like what she experienced, can be understood as being what it is - totally wrong and unacceptable. With good input from the professionals about her, she will be able to deal with this, as will you too.