My tortoise hasn't yet emerged from hibernation but has her head out and has a very fat neck. Does anyone know what the problem is?

Hello,
The main problem is not the neck, it is that it has not emerged from hibernation.
Steadily warm it up & when it is properly active, place it in tepid water for at least 10 minutes. Let us know what happens. Also please give full details of:- species, age, how long you've had it, method & length of hibernation,etc.
Regards
Tom