If your mother needs to apply for Medicaid, the state will count the current value of this stock as an asset of hers. Unless you can prove that it is worthless or legally impossible to liquidate, that value will count toward the $2,000 maximum she is allowed to possess and still qualify for Medicaid for long-term care.
At this point, I agree with you that you need to escalate the formality with Company B and try to find out how you can sell the stock. Perhaps the assistance of a local stockbroker can be helpful, too.
