The five-time British champion saw off her rivals to win in the three-metre springboard.
Gallantree missed her second dive in the final but hit back in the third round with her front three-and-a-half somersaults piked.
She finished with a score of 304.20, while her City of Leeds club team-mate Katherine Torrance got silver and Plymouth’s Rhea Gayle settled for bronze.
“My reaction is a little bit mixed,” said Gallantree. “I did two really good dives which I am really happy with, but then the other three weren’t so good.
“The younger divers are coming through really quick.
“I mean Katherine is looking great, who was in second place and Rhea pulled out a really great performance. The depth in women’s springboard is amazing.
“Four or five years ago there were a couple of divers at the top and then there was just no one behind, but now we’ve got so many girls pushing those big scores and it’s fantastic.”
Double Commonwealth champion Jack Laugher claimed his second title with victory in the three-metre springboard.
The City of Leeds diver’s total of 462.65 on the second day in Plymouth saw him edge out club-mate Chris Mears – with whom he won synchronised gold on Friday – with City of Sheffield’s Jack Haslam some way back in third.
“In the final my first two dives were probably the best I’ve ever done them then things went downhill a little bit, but I tested out a new dive (yesterday) and it’s the first time I’ve ever done it in competition,” said Laugher of his front two-and-a-half somersaults triple twists piked effort.
“I also think it’s the first time a British male has done it and I got 91 points in it which is pretty cool.”
Lois Toulson, aged 15, won her first British title with victory in the 10m platform, beating European champion Sarah Barrow into second place.
“It feels fantastic to be British champion. I never expected it so it’s great,” Toulson said.
City of Sheffield duo Millie Hafferty and Millie Fowler won the three-metre synchro, while City of Leeds’s Matty Lee and James Denny claimed first place in the 10m synchro.
Elsewhere, Tom Daley marked his return to his hometown of Plymouth in the best possible way by taking gold and there was a tremendous buzz at the Plymouth Life Centre yesterday.
Daley, the Olympic 10m platform bronze medallist, unveiled his new twister dive – a forward three-and-a-half somersaults with one twist pike – that no one had performed before.
The 20-year-old, whose highest scoring dive was the front four-and-a-half somersaults tucked with a mark of 96.20, finished with 493.70 points to secure his second national title.
He beat 14-year-old Matt Dixon, while Matty Lee got the bronze.
“I dived pretty well considering it was the first competition I have done in about five months,” said Daley. “Everything was steady, nothing was amazing but nothing was bad, but I’m looking forward to building on that in the competitions to come.
“My dive, the new twister, went pretty well actually. It was all there. I could have done a little better on some of the elements, like getting my entry better, but that all comes with a new dive.
“The more I do it, the better it will get.”
Daley, who moved to London to train a year ago, is looking forward to competing at the World Championships this summer in Kazan, Russia.
“It’s the first opportunity to qualify for the Olympic Games so I need to make sure I’m in the best shape,” he added.
“But we’ve got the World Series before that, so there are lots of chances to practice my new dive and make sure that I am in the best competition shape.”