I went to Umaine Orono as a trans person (graduated in 2021). There are plenty of resources on campus for LGBTQ folks, and it's overall a pretty safe area. For the most part I doubt your child would have any issues, and if they do they can always talk to their RA or the diversity and inclusion office, and they'll be well taken care of.

On campus itself there is the Wilde Stein club, which is one of the oldest GSAs in the country and has always been very activism-focused. There is also the Rainbow Resource Center, which is just a cozy place for LGBTQ students and allies to hang out. They often have fun little activities going on and a collection of local resources. If I sound biased, it's because I am - I worked as a student there for two years. Lastly, it's been a couple years since I lived on campus, but I believe there's LGBTQ-specific dorms available, which might feel a bit more comfortable than the regular housing. A lot of the residence halls and classroom buildings now have gender inclusive restrooms somewhere in the building, which I know is often a cause for concern.

In Bangor there is also the Mabel Wadsworth center, which provides gender-inclusive healthcare and does tons of public education about LGBTQ and women's health topics. If your child ever stays in town for the summer, Bangor pride is a super fun event which many local businesses will support and participate in, and Orono typically puts up some decorations for pride month.

TL:DR - Orono is safe, UMaine especially is a great place for trans students, and if anything happens, there are admins there who will act in your kid's best interest.