Also, what size viv? In my opinion any viv (I've never seen any smaller than 18") is too big for a 09 corn.
I still have 08's in RUBs.
As for when to start worrying. Weigh her, follow her weight weekly and if she is losing weight - worry. If not keep doing what you are doing.
5.2.0 Corn snake 3.1.0 Milks 0.2.0 Kings 1.0.0 Northern Pine 2.0.0 House Snake 1.1.0 BREDLI!
3.1.1 Yellow Bellied Slider 2.0.0 Cumberland Slider 1.0.1 River Cooter 0.0.1 Mississippi Map 0.0.2 Common Musk
2.0.0 Chocolate A.P.H 0.3.0 Lovely Rattie Girls