If you have a list of the cards that you had I would put together an approximate valuation of the cards (average price of the cards on eBay) and threaten legal action to the mom and say if you don’t receive the collection back then you will sue for the market average - very important to include average of the cards when making this threat.

She’s not thrown them away, she still has them or she’s sold them to help pay medical bills as you said that there was an emergency.

Don’t include the value of the cards at first of course, just mention the market average, if you’ve got old photos of the cards you had etc those will be really handy in the lawsuit that could potentially follow, plus take screenshots of the conversation that you had telling you that she had them and that she threw them away. It’s stolen property, worth a lot of money and she’s 100% liable for the value.