We have had or Herman tortoise for 4 yrs and she has decided to hibernate this year, she hasn’t done this before. I’m worried she is unwell - is this normal behaviour?
They don't "decide to hibernate". If you haven't spent the time emptying the gut, and gradually bringing the heating and lighting down, and then keeping the temperature consistently low, then the tortoise isn't hibernating. Also, I was recently taught that tortoises actually brumate, not hibernate.
What size enclosure? Indoors or out?
What are your four temperatures? Warm side, cool side, basking area, and over night low?
If your tortoise is just dug in in its indoor enclosure and not coming out to eat, that indicates a problem, but it is not hibernation.