Got the verdict this week. A sow which I bought in-pig from a very good breeder had a nice litter in December but, since then, proved impossible to mix with any others in the herd (she killed one sow), including boars.
Tried three boars, but she beat up every one. Three strikes and you're out here (even though she was a lovely, friendly, people-orientated pig).
Anyway, the abattoir confirmed my decision to cull - she had cystic ovaries, clear from the calcified eggs.
That explains the behaviour problems etc. Mind at rest now!