If she will switch, I would definately get her on rats. Some are just mousers for life. Rats would be ideal, you could then feed an appropriate sized meal, with one item. If you stay mice, you need to feed multiple. Typically the rule of thumb is either a rodent the same size as your snakes widest part, or a rodent that is 10-15% of your snakes weight. But if she is that old and only eating a mouse every 2-3 weeks, that's not enough. My grown bps get offered a small rat every week.
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