Avil is the 2007 junior European and world champion
Will Clarke and Hollie Avil laid claim to British Triathlon titles in Wales, two days before their Olympic flights.
Avil, 18, built up a healthy lead on her bike in the Welsh venue of Bryn Bach Park, then held on in the 10km run to see off challenger Liz Blatchford.
"This caps off an excellent week," said Avil. "I'm really looking forward to China and getting on that plane."
"I can't believe it, I felt so good out there," said Clarke, who held off GB duo Tim Don and Alistair Brownlee.
Don and Brownlee kept pace with Clarke, alongside Stuart Hayes, for much of the 1500m swim, 40km cycle and 10km run, but Clarke pulled through.
"I wanted to win, but left my charge a bit late and Will was awesome," admitted Don, who forms Britain's five-person triathlon team alongside Clarke, Brownlee, Avil and world champion Helen Tucker.
The athletes now fly to the Korean island of Jeju on Monday for their Team GB preparation camp ahead of the Games.
The Olympic triathlon will be held at the Ming Tomb Reservoir, to the north of Beijing, on 18 and 19 August.