Hi,
Is your snake normally interested in fish? When mine was younger, he loved feeder guppies and then as he got larger (about a year old) suddenly would lose interest in them for long periods of time. We switched to bait minnows (this was before I knew about some fish being dangerous for garters! We just got lucky that these were apparently a good species) which he ate well because of their larger size.
Also, it was around this time when he would start to go longer without eating, so like other people have said, if she isn't losing weight you probably shouldn't worry.

Good luck getting her to eat!!