Hi, thank you for the query and Welcome to HCM forum.
There are many possibilities that can cause left hand swelling. Congestive heart failure
usually causes difficulty breathing
and swelling of the dependent part of the body like leg and lower back region, though it can cause whole body swelling. but only left hand swelling from CHF is less likely. Another consideration is obstruction to the venous flow by some sort of external pressure during sleeping that cause morning swelling and it improves throughout the day as this time patient is mobile. Infection like cellulitis
can also cause swelling as there is positive history of cat scratching.
So, for complete evaluation you do need to consult with a doctor as physical examination and some investigations are required. Hope, this helps. Bye, God bless your mother.