Tortoise suddenly doesn't like the UVB bulb?

I have a Russian tortoise female, approx 15 yrs. The bulb is a reptisun 10.0 CFL. She also has two heat bulbs, all on 14 hr daylight timers.

The CFL is about 5 months old.

Three weeks ago, she started hiding under things and not eating whenever the CFL bulb was on (did not eat for a week originally). If I turn it off, she starts eating the next day, and eats extremely well. I tested the theory 3-4 times with different time intervals, and always the same results.

Now, any clue on why this is? The bulb is getting close to the magical 6 months expiration, but that means it should decrease the UVB, correct? No signs of eyelid swelling, etc, she looks normal.

Temps are gradient and kept at ~65 at the colder end, 90 directly under the lamps. When she hides, it will be at the warm or cold end, no preference, as long as she can get under something. No recent changes in diet, temps, substrates, etc.

Any suggestions would be helpful! I don't want to spend the money to buy a new bulb if will just hide from it, and it is too cold up here to be adding natural daylight for a few more months.

Thanks in advance!