Corn snake has a medium sized lump

Question
I have a 11 year old corn snake.
It has all the correct heating, lights, substrate etc
She hasn't eaten for about 6/7 months now although we have tried her on rat pups and chicks although her normal diet was large mice and recently i found a noticeable enlargement of the body about 3/4 down and about an inch in length
Her behaviour hasn't been affected she is still really active trying to escape when the glass doors are open and eager to be held
the lump is quite hard to touch and hasnt got any sort of outside abrasions so know its not infection of any sort.
Over the month that we have been monitoring it, it hasn't grown in size
Any help appreciated
If helpful i may be able to take a photo and attach it, ask if needed or prefered

Answer
Shaunna,
  If you have had the snake for years, I do not doubt your husbandry at all/ 6 to 7 months is way too long for a snake 4-5 foot. In fact, I have never heard of a snake that small going that long without eating. I would take her to the vet ASAP. Please note that I am not a vet, just an experienced keeper.