Tessa, welcome to the forum! Always nice to have international friends join us! I don't know a lot about your weather, but it's probably safe to assume you'd be maybe a zone 6 or 7, getting to freezing in the winter from about now to maybe April?

Plumeria seedlings will not go dormant their first winter, but most do their second winter. You may find a mix of dormant and not-dormant. Just water the ones who keep most of their leaves only when they look like they need it. That will vary a lot depending on the temperature and humidity level you provide. Those who lose all or nearly all their leaves can do without water pretty much all winter.

Your seedling looks great and may still be small enough to not go dormant. It looks very like the only one of mine to branch from the 2010 crop. Here it is earlier this year:

Only the main stem grew much. To be safe I've recently tied the outer branch to the main branch, to grow more at a 45 degree angle and to keep it safe with all the winter moving that's coming up.

Good luck and let us know how it goes!

Hey Jandey, thanks for your response! Ultimately both my plumeria went dormant so I let them dry really well before moving them to a slightly colder room I do keep them in the windowsill because I heard keeping them near light is best. So far so good (no rot yet) Can't wait till they start growing again!