The ziploc bag should not affect the smell if it is actual spearmint. I have the kind you are talking about as well, you can put a leaf in your mouth and it tastes like gum, and I've put it in a bag and it still smelled strongly like spearmint. There are many varieties of mint and the leaves all look similar, it is possible she gave you a different variety. I only grow spearmint and peppermint so I don't know anything about the other varieties, maybe someone who knows more will chime in. Is it possible that you could take them to a nursery and see if someone there could identify it?