Gee that's a good question!
It would be an extremely strange situation if that happened, wouldn't it!
The jury (of 12) find her guilty (with a majority verdict of 11), of the attempted murder of Ian but are unable to find her guilty of murdering Gail, Heather and Don due to not being unanimous (as 12).
My feeling is, since all the victims were at the same lunch, the jury will be considering the 4 separate verdicts the same. So, there probably wouldn't be a 'not guilty' verdict for the murder of Don but a 'guilty' verdict for the murder of Gail, for example. Common sense would say that the same would apply to the attempted murder of Ian.
I don't think the jury would ever get to that strange predicament, even though the way I read the rules, it's technically possible.
MOO
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