because lightning is opaque to surveillance (by design) it is impossible to really know exactly the volume of transactions. we know that there is well over 5000btc of liquidity on the network and it's entirely plausible that at least 1000btc moves back and forth daily, which comes out to 10MUSD daily which gives you a figure of about 3 trillion per year

so she's not just plucking numbers out of the air, they are in range of plausible