Hi Jasper...
Sorry to say, but I really surprise in which time you live on this Earth. Its 21th Century dear... Please Wake Up...
I really don't understand your problem. Why you consider Saree as an offensive Dress?

In my views, Women always look their best in the sarees. A saree combines grace, beauty & elegance. Above all... Wearing Saree is the most perfect and simple way to let others think that you are true Indian Women, with moral values and that you respect your tradition.
You should be proud of your Mom that she gives so much values to her culture, her traditions. In todays world when women are more and more trying to expose them by running towards western dresses and western culture, Your Mom is still maintaining her Dignity.
Men will always like a Women with such moral values; may be that's one reason, your friends talk about her. Why don't you give strict warning to your friends instead of making your Mom change her way.

Hey one thing more, Its Human Nature to explore the hidden secrets. If every thing is behind their eyes, they will never give it a damn look. Hope you understand my point here...