How can I encourage a gopher snake to eat?

My boyfriend's gopher snake has been refusing to feed for around two months. She used to have a very active appetite and would go for live or frozen mice. She has shed normally, has no external injuries, does not appear super thin and has a proper cage temperature, but she has not eaten for several weeks. We can't seem to find any store that has Zilla Jump Start reptile appetite stimulant in stock, so that route has failed. Does anyone know a site that has this product in stock or a similar product for snakes? Are there any foods that might encourage her to eat? She currently lives in harmony with a younger male gopher snake, but he is perfectly healthy and eats very well. Any advice?