Why Did Carly Fiorina Accept $500,000 From a Ted Cruz Super PAC?

Ted Cruz has a stable of super PACs supporting him. One is called "Keep the Promise 1" and it did something odd a few months ago: it donated $500,000 to Carly Fiorina. I missed this at the time, but an FEC letter has brought it back into the spotlight:

Keep the Promise 1 had a healthy $10 million on hand from a $11 million donation from hedge fund CEO Robert Mercer as of the end of June. But it only spent $536,169. A little for legal services. A little for surveys. And a whole lot for Fiorina.

....The donation to Fiorina was made June 18, which shows tremendous foresight. Fiorina was barely registering then, not yet revealed as the scrappy underdog with killer debate skills. And Donald Trump had yet to steal most of Cruz’s disenchanted voters.

Nobody knows why a Ted Cruz super PAC would donate half a million dollars to Carly Fiorina's campaign. But that's not what I'm really interested in. What I want to know is why Fiorina's campaign accepted the donation. Fiorina has shown an impressive aptitude for tap dancing and misdirection, but I don't think even she can pretend that a gigantic check appeared out of nowhere and they didn't bother asking any questions about it. So what's the deal, Carly?