Amanda, who is based in America, underlined an impressive run of form this year by winning the 1.50m jump-off class, sponsored by Horseware Ireland.
Eleven combinations went through to the jump-off, and it was Amanda who triumphed on Luibanta BH in a time of 33.30 seconds.
That proved enough to edge out the challenge of Irish star Shane Breen, a winner earlier on Saturday at the Echo Arena, who finished 49 hundredths of a second behind with Ipswich van de Wolfsakker, while another Irishman - Conor Swail - took third aboard Domino van de Valhoeve, and Britain's Robert Whitaker fourth on Catwalk IV.
"She is a super horse," Amanda said. "I have three mares, and they all seem to go well.
"It is so special to to do this and win here. It is the first time I have jumped in England since I moved to America, and it was great that a l,ot of my family and friends came to watch.
"The horse has done everything and more that we could have hoped for. She has been my best horse this year. She did two indoor shows in October, and then had a bit of a rest before I came over here.
"She never gets flustered. She is easy-going. Anything you ask her to do, she just seems to go ahead and do."
Puissance winners Chris Megahey, Holly Smith and Louise Saywell all paid tribute to this year's Liverpool International Horse Show after they produced a thrilling Saturday night finale.
A capacity crowd at the Echo Arena revelled in a high-class competition that saw all three riders - Chris on Seapatrick Cruise Cavalier, Holly with Quality Old Joker and Louise on Dassler - clear a fifth round height of seven feet two inches.
The class, sponsored by Equitop Myoplast, is always a firm favourite among spectators, and once again it did not disappoint.
"I've had the horse for four years, and been really successful with him," Irishman Chris said. "I've been here every year of the Liverpool show - I think I was third in the puissance in the first year - and it is such a really good show."
Four combinations made it through to the fifth and final round - with the famous red wall built to a jaw-dropping 2.20 metres - and three went clear to ensure a share of the top prize.
Reflecting on her performance, Holly said: "Quality Old Joker is a great jumping horse in his own right. He was third in the Hickstead Derby this year.
"All my horses have gone really well this week, and I am delighted."
And Louise added: "The horse is very scopey, and I know he can do it in a class like the puissance.
"I've been coming here for three years now, and Nina Barbour and her team put on a fantastic event."