They are magic beans, so maybe her WL magic would not work as that was size change magic for people. Gold did not mean other beans but other outsiders I thought.
The plant Regina left in her office might have a root for a cutting. Why did GOAT not destroy the plant when they took Regina? I suppose they were in a hurry and didn’t realize a cutting would work, plus maybe they had planned to blow up the town/magic some other way than the failsafe. Cuttings don’t always grow if not handled properly and even fast-growing beans presumably need some weeks and giant/dwarf loving care.
“If I had a world of my own, everything would be nonsense. Nothing would be what it is, because everything would be what it isn't. And contrary wise, what is, it wouldn't be. And what it wouldn't be, it would. You see?” -- Lewis Carroll, Alice's Adventures in Wonderland & Through the Looking-Glass