My mom is in her mid-60s, she immigrated from Russia to US.
She has like $130k in cash, under her mattress (not literally).
How can she put this money to use without alerting the IRS, etc?
You're effectively going to have to launder it.
One way to preserve its value against inflation would be to buy chattels like silver cutlery, silver candlesticks, paintings, or swiss watches. Richfags have been avoiding inheritance tax in this way for a long time.
My advice would be to start a small cash business. Buy very cheap plastic shit and sell it for twenty times the price. If you have access to a garden, you could claim to have been selling home-grown vegetables, in which case all you would need to do is buy a few sacks of seeds and fertiliser to give your business the receipts needed to explain how it made its money.
You sell invisible organic carrots to invisible customers in cash, take a small hit on corporate tax, and legitimise your money.
That's not the same at all, did you even read it? It says US citizens and US residents who live outside the US must pay US taxes on all worldwide income. No part of that applies to OP's mom. She doesn't live outside the US, she just moved to the US. And she didn't earn any income, she merely has savings.
Here's an actually relevant link: https://www.irs.gov/Businesses/Gifts-from-Foreign-Person
A US citizen/resident receiving a gift from a foreigner in excess of $100,000 must report it. But no tax is due. Why? Because the person giving the gift is the one subject to the gift tax, not the person receiving it. In this case the person giving the gift is not a US citizen nor a US resident and therefore no taxes can be levied on them. She can report the 130k on form 3520 as if one of her relatives back in Russia gifted it to her, and no tax is due.
if this chart wont convince her then i dont know what would