It is easy to get stuck in the Dead End. If she asks for ten diamonds, and you either do not have them or simply do not WANT to sell them to her, she will never ask for anything else.

It does not mattter how many times you close and reopen the software, how often you skip time at a campfire, how many Blood Moons have passed, how far you have progressed the story in the meantime - she WILL continue to demand ten diamonds, period. The only way to get out of that dead end is to GIVE her ten diamonds and complete the current trade cycle so that she rerolls her demand.

… which might result in diamonds AGAIN if you’re unlucky.

And all that for a mere 10% extra, whch amounts to 50 rupees per diamond and noticably less for the other gem types. That’s pocket change at best.

Of course it can’t hurt to sell a surplus of gemstones to her if she happens to ask for something that you already have and are willing to part with anyway, but if you just want to sell 50 sapphires to her and she continues to ask for the “wrong” gemstones so you have to go out of your way to farm more over and over again … that’s simply not worth the hassle IMHO. You’re better off selling your gems to literally anyone else.

PS: Yes you can trade ten Luminous Ore to the Zora Stonemanson Ledo to recieve a diamond, but that will make you lose money. A diamond sells for 500 rupees, Ramella will buy them for 550 rupees a piece, but the ten Luminous Ore sell for 700 rupees total, so you lose 150-200 rupees for every trade.