Your only other option besides looking would be to possibly see if you can "feel" the embryo's with in her, but this usually only works with a snake that's really far along. Besides that, your only other option would be an ultra sound and I'm not sure they can even do that with as small an animals as a garter (I've seen them used for anacondas before!). As far as looks, you garter will be noticely heavier, but most of the weight will be carried further back on her body....say perhaps a third of the way up from the cloaca. Hope this helps.

Roy