I personnally have no problem with keeping garter snakes as they are very common, unless they are threatened or endangered. One thing you should do though is if she has babies to release them where you found mom.
One other thing you might want to consider before keeping her for too long and its too late to release her. Garter snakes go into hibernation all of the winter. There is no doubt in my mind that she has been alive for a few years and has hibernated. This is a natural cycle to garter snakes and once it has kicked in one year it will continue every year. A garter snake her age will stop feeding as winter approaches. With the onset of wanting to hibernate you will have to be able to set up hibernation quarters for her so that she can hibernate through the winter months. If not she can die as she may not want to eat any longer. Hibernation is a big step that collectors tend to forget about these northern species. Once they have gone through it, they will usually want to continue the cycle every year. It not only keeps them healthy but it also makes way for the new breeding season.
Decide if you can set something up for the winter months for her. Here is a simple layout:
A plastic bin with a tight fitting lid. Holes in it for ventilation of course
Leaf litter
A Basement or place that will get to about 45-55 degrees and remain that temp all winter. and then rise slowly to normal temps. An Ideal place is a shed or unheated basement. Nights that reach into the low 30s doesnt seem to hurt them as long as they dont remain that low for too long.
You must be able to keep a fresh water source with the snake and be sure it cannot be knocked over.
Regular check ups every week to see how she is doing.
ALSO and one of the most important! : Prior to the onset of hibernation....no feeding two weeks before she goes into hibernation. She must be clean from the inside. If she goes into hibernation before all waste is clear she can die.
Hope this helps a bit,
Lu
