First, she gets a massive tax receipt to use against other income. I don't know how it works in the US, but in Canada you can use charitable tax receipts to lower taxable income in future years if you don't want to use the whole thing in the year in which you made the donation.
Second, she donated to a donor advised fund, or DAF. A DAF is a charitable entity that is sort of like a bank account: you put your money in, get the tax receipt, your money manager invests the capital, and you can allocate some portion of the money (the amount depends on the financial institution's policies) to actual 501c3's (I.e charities doing charitable work).
DAFs are just another instrument offered by the Fildelities of the world to increase assets under management.
The most common reason people give to DAFs is so they can get a tax receipt for the current year and defer the decision about which charities to support until later.
Plus giving stock to charity is the most tax-efficient way to give. She gets the tax receipt for $148m regardless if the stock goes down after the donation. And if it goes up, she has more to give to charities.
I've Had a long term contract to build an online donor advised fund, so my head has been in this space for 8y or so.