Just 12 months on from completing her first shot at the world-famous three-day event in fifth place, the Hallington rider finished two positions higher aboard AllStar B.
The pair have put together a string of top-10 finishes in elite four-star competition and were in contention all the way through in Gloucestershire.
“I think it hasn’t quite sunk in yet,” she said. “I’m a doubter and can be quite nervous so I have just tried to take every day as it comes and only when I came out of the prizegiving did I realise what I’ve achieved and what I could achieve.”
They led after the first of two days of dressage with a score of 23.9 on Thursday.
“He has the most amazing mind and he allows me to ride him in a way that creates a lovely picture for people to look at,” she said.
Canter hadn’t ridden the test in more than two weeks, following the advice of her trainer Ian Woodhead.
“I sent him a video of me riding through the test on Allstar B and asked him what he thought,” she added.
“He told me it looked brilliant and that I shouldn’t practice it any more. It made me nervous not spending all last week going through the movements, but Ian was right.”
Allstar’s score was eventually eclipsed, narrowly, by Oliver Townend and New Zealander Mark Todd after the tests were completed on Friday, but just three marks separated the top three going into Saturday’s cross country.
The 32-year-old held station in third after getting round the tough cross country course with just 6.4 penalties, the joint-fifth best round of the day as Kiwi rider Jonelle Price soared to the top after picking up just 0.4 penalties.
Needing a clear round in the show jumping finale to stand a chance of victory, Canter had just one pole down, but finished behind Price who kept her cool to go clear and take the coveted crown.
The Lincolnshire rider finished just 6.3 points behind the winner and just 1.2 adrift of runner-up Townend.
“He’ll have a little bit of a break, and World Equestrian Games or not, he’ll aim for another big one this year,” she added.