I am not a great fan of tarantulas. No offense. One of co-workers has one though and he said his has not eaten in almost a year. Which is difficult believe, but..whatever. I think it has something to do with them molting, maybe? Check out Tarantula Com., you can probably find some good info there.
Your G. rosea is fine. I have a 13 year old that has fasted for over one year. They are notorious for long periods of not eating. Though this can make for a boring pet it is the natural behavior of the animal. A good way to determine if it is getting enough food is to keep an eye on the abdomen. If it gets much smaller than the carapace it needs to eat. The low caloric intake of this species contributes to the incredibly long life span of up to 30 years!