Why might my iguana be freaking out lately?

I have a 2 year old green iguana. I'm pretty sure she's a female. She's about 2 and a half feet long (snout to tail). I've had her for about 5 months, and she's always been very docile. She would let me hand feed her, pet her, hold her, even take her on walks outside. But the past few days, when I walk into her 6 foot by 4 foot by 4 foot enclousure, she leaps off of whatever she's on and starts flailing around and freaking out. She never used to do this before, I would normally be able to walk right up to her and pet her or even pick her up and take her out with me. Why could this be? The only thing I can think of that might be spooking her is a new fake tree that I put in her cage for her to climb on, but she started tweaking a few days after I first put it in there. Any help would be greatly appreciated, I love her to death.