Qualifying long term care insurance is part of the health insurance that can be excluded from employee wages and deducted by the corporation. See Accident and Health Benefits for details.
As you may know, benefits paid to more than 2% shareholders of the S corporation are generally not deductible by the corporation. See 2% Owners for more details.
Sec. 318. Constructive ownership of stock says:
"An individual shall be considered as owning the stock owned,
directly or indirectly, by or for -
(i) his spouse (other than a spouse who is legally
separated from the individual under a decree of divorce or
separate maintenance), and
(ii) his children, grandchildren, and parents."
So, your mother's benefits can not be deducted by the corporation and excluded from her wages (similar to yours) since she is considered as owning the shares that you, her child, own.
Of course, the corporation can pay the premium and include that as wages to your mother in order deduct those amounts the same as other wages paid to her. The only caution might be that her compensation for the work performed will have to remain "reasonable".
I hope this helps to know the rules for deducting benefits and the stock attribution rules; even though it may not be what you would have liked to hear.
Please ask if you need clarification. Thank you.