Had security agents not relented, she said on her Web site, she might not have flown, she said in a posting dated Wednesday.
"I don't know what I would have done if they hadn't — sailed home probably," she wrote.
The author had participated in a book reading for charity on Aug. 1 with fellow writers Stephen King and John Irving. Security was drastically tightened after Aug. 10 when British police said they had intercepted a plot to blow up U.S.-bound airliners.
"The heightened security restrictions on the airlines made the journey back from New York interesting, as I refused to be parted from the manuscript of book seven.
"A large part of it is handwritten and there was no copy of anything I had done while in the U.S."
Eventually, she added, "They let me take it on, thankfully, bound up in elastic bands."
Rowling said she was still considering two possible titles for the last of the boy wizard's adventures.
"I was quite happy with one of them until the other one struck me while I was taking a shower in New York," she wrote.
"They would both be appropriate, so I think I'll have to wait until I'm further into the book to decide which one works best."