You are asking your dog to take daily abuse and just put up with this.
I think your son needs training as well as the dog needing training work and a safe place to go that your son will not abuse her while she rests there. You can set up a crate for her or pick a room and make that her space that no one can bother her when she is there.
You should have your vet check her out as she may be irritable due to arthritis pain or another health issue.
The work you are doing with the dog rolling over and the child grabbing her throat are very likely to make all this much worse and its not teaching the child to be gentle with the dog.
I do think if nothing changes you are heading for a real disaster as the dog is going to be hurt one time to many and retaliate in a clearer manner to get respect from the child as the 'warnings' have not worked.
You may want to work with a trainer to get some family help on this.
www.apdt.com may help you find a local trainer to work with.
You might ask yourself how many hours of your son's rough play and handling you would cope with before telling him to stop and making him stop if he didn't. If your son kicks you in the stomach or hurts you how good would your temper control be? The only way the dog has to say stop that you are hurting me is with its actions. If your son doesn't listen she's just going to say it 'louder'. So yes the next time could be worse and even the sweetest dog in the world of any breed might not put up with abuse forever.
Hope this helps you!
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