Answer in Details
Nowhere in the teachings or stories of Lord Shiva is it suggested to deny food or care to one's mother, especially if she is in need or unwell. In fact, serving your parents selflessly is considered punya (meritorious act) and brings blessings. If someone claims that God told them to deny food or care to their mother, that goes against the very spirit of dharma and Shiva's teachings.
If your mother has had an operation or is unwell, it is your sacred duty to care for her, feed her, and ensure her well-being. This act itself is a great service to Lord Shiva, as He resides in all living beings, especially in one's parents.
May Lord Shiva bless you with strength, compassion, and clarity. Om Namah Shivaya.