No, that's not what happened. She didn't own any shares of AMC. She sold naked call options of AMC.

I will try to explain this as simply as I can, this is a simplification of options trading.
A call option is a contract. Typically, in a call option, the buyer will pay a fee to the seller of the contract known as the "premium". In exchange, the buyer has the right, but not the obligation, to purchase the underlying asset from the seller at a certain price ("strike price") at a certain time. For example, Brad buys a call option to buy one share of XYZ stock with a strike price of $40 and pays a premium of $2. If the share price goes down to $30, the contract isn't exercised, Brad loses $2. If the share price goes to $60, then Brad can exercise the contract and pay $40 for a share that is now worth $60, netting an $18 profit after taking into account the premium.
On a
covered call option, the seller writes a call option on an asset they already own. Some high IQ cels use this to earn money from option premiums by engaging what is known as a "buy-write transaction", by simultaneously buying an asset and writing call options on it.
On a
naked call option, the seller writes a call option on an asset they don't own; if the contract is exercised, they will have to themselves buy the asset at its current market price in order to sell it to the buyer of the call option. Let's use the same example we used above: Stacy sells a naked call of XYZ to Brad with a strike price of $40 and a $2 premium. If XYZ falls to $30, the option isn't exercised and Stacy earns the $2 premium. But if XYZ rises to $60, Stacy will have to purchase XYZ at the current market price of $60 so she can sell it to Brad at the strike price of $40, netting her a loss of $18 after taking the premium into account. As you can see, selling naked calls is extremely risky because if the share price skyrockets, you will get fucked.
That's what happened. The Redditor foid sold a lot of naked AMC calls thinking that AMC would fall below the strike price and she could earn money from the premiums, but AMC rose by 98% in the span of a few days, and the buyer exercised the options. Obviously, TD Ameritrade, the broker, couldn't simply leave the buyer out to dry, so TD fulfilled the contract and billed the femoid for the price differential of the AMC shares they had to buy -- about $650k worth.
She gambled and she lost, she didn't hedge by buying some call options herself, she has no basic concept of risk management, I mean I don't know what to say, this is so fucking stupid.