If you've been on the health and hygiene forum you've seen that my little Curious has been sick. I've began taking her to an exotic vet in Cream Ridge, NJ and she said in order to be healthy, females need to breed at least once a year. Is this true? I've never heard of this before and it is making me question my vet's familiarity with sugar gliders.

I don't think so, many, many, many females have never been bred at all and have lived long, happy, healthy lives.

My oldest female only bred twice and it actually exasperated a health issue we didn't know she had, so she was never bred again (she is 9 yrs old now, has not had joeys for 7 years).

I have females that have never bred as well. They do not "need" to breed to be healthy happy gliders.

I am of the understanding that some female animals of other species are so biologically ingrained to breed that they will undergo "false pregnancies" if they do not breed. I cannot say why they do this, but I know a false pregnancy is very dangerous.
Sugar gliders seem to do fine and I have yet to hear report of health issues related to NOT breeding, but I have heard plenty of issues that can be caused when breeding,

To the best of my knowledge, it is not necessary for a female to breed at all to be a healthy glider. I would definitely look for another vet.

You may find vets listed at Sugar Glider Help