G'day my English friend,
I'm sorry to hear of the situation with your daughter.
I can assure you that the shunning procedure would not apply to your daughter, for as you rightly say "She's never been a JW". So, organisationally, there is no treatment of her, whether good or bad.
So any ostracising of her is being done on a personal level i.e. your mother is using her 'Bible trained conscience' Both peaceloveharmony and Had Enough highlight the matter of 'worldly' (i.e. non-JW) associations. The R&F have an obligation placed on them by the Borg to demonstrate their loyalty 'to the organisation' by avoiding such contact. At least, from what I have seen this is how it's interpreted by many.
Probably your mother feels she is demonstrating her love for Jehovah by following the course she has. Of course, we all know that Jehovah's Witnesses don't break up families, don't we?
Didgeridoo suggested talking to your mother about it. Perhaps her conduct has never been discussed. She might even have a twinge of conscience after you speak with her about it.
Good luck.
Ozzie
Freedom is not having to wear a tie.