Plumeria are deciduous. Losing leaves in the winter is normal. Also losing leavings in the summer is not a cause for concern as long as it is the older leaves. Yours is probably just fine.

Mike

Be real careful with watering it if it has gone dormant and lost it's leaves. I only water mine 1/2 cup for a 1 gallon pot once a month during the winter when they are inside. The fastest way to kill it is keeping it too wet. Even though the top of the soil is dry the bottom my still be wet. Good luck with your plant and let us know how it does. Welcome to the group.
Peg

Zell, unfortunately your plant will suffer from the longer indoor winters in Vermont. They only need 2-3 months of winter rest and as much sun as possible the rest of the year to be at their best.

Can you give it some supplemental lighting to keep the dormancy period shorter? This will give you a better chance of blooms as the plant matures.

Good luck!