Hmm,
I was wondering if she was feeling nervous and, basically, getting ready to pee on you to make you put her down.
But if you have had her that long and she is fine with handling then it probably isn't that.
Have you noticed any thread or worm like things in her poop? Just wondering if it could be parasites irritating her vent - also for a similar reason it might be worth checking for stuck poop or substrate inside her vent if you can catch it open.
dr del