director disputes and lazy partners

[GLU23]

My sister has a very unreliable business partner. There are three shareholders in the company - my sister, her ex-husband and this other person. Her husband left the company and the marriage just weeks after it was formed. He took his name of the lease (its a pub) but didn't allocate his share of the limited company to anyone. In the meantime, my sister has struggled on with this very unreliable person. They both operated the business but on at least a dozen occasions when it was supposed to be my sister's time off, her partner wouldn't show up to open the pub, or would walk out mid-shift. In October she disappeared and took £20,000 from the business account to pay for four weeks in rehab. First she said that she was depressed, then she said that she had an allergy to alcohol and now she says that she's a recovering alocoholic. She came back six weeks later wanting to come back to the business but my sister, her staff and the customers don't want her back at work and my sister doesn't want her in the business full stop. While she was gone, my sister's ex signed over his share of the business to her giving her a two thirds control of the company. She has just received a solicitor's letter telling her that the share transfer is illegal and her partner is demanding that parity be restored between them. My question is two-fold. First is the share transfer illegal and second can her partner be proscecuted for fraud in any way.