I found the source of my info about JA's dancing skills: an essay by Stuart Tave called "Limitations and Definitions" in the Norton Critical Edition of P&P, 3rd ed. The essay begins:

"Jane Austen was fond of dancing and excelled in it. She often writes about it in her letters. (snip) In the earliest letter of hers that survives, written when she was twenty, she says, "I danced twice with Warren last night, and once with Mr. Charles Watkins, and, to my inexpressible astonishment, I entirely escaped John Lyford. I was forced to fight hard for it, however."