This is apparently her new pitch because she said the exact same thing to Hollywood donors the day before.
Via Weekly Standard:
First Lady Michelle Obama tells rich donors to keep the checks coming. “You can write a check. Or another one. Write a big fat check. Write the biggest check you could possibly write,” the first lady said at a high-dollar Democratic fundraiser last night in San Francisco.
“Some of you might be tired being always asked for money,” Obama added. “I know that writing those checks is the single most impactful thing you can do right now.”