I heard that some of the cities in India are so poor that there is a danger of kidnapping for ransom by desperate bands of people. I don’t think that is true in the mountain regions. If mace is in a pressurized canister there might be a problem with it in a non-pressurized baggage compartment. Certainly the airlines could inform. The other piece of knowledge that might be useful is what the laws in India say about the use of Mace. Is it legal to possess Mace? Can one transport it in a backpack? Who can it be used by and upon whom?
If your sister is hiking solo is there an outfitter in India who she is getting supplies from? Does the trek in India have other hikers who begin from a particular point. On the AT there are two ends of the trail where many begin but then some begin at other points of the trail to do a section. Is there similar tradition in the part of India where your sister will be hiking?
How did your sister decided to hike where she will be hiking? Is there an organization that suggests hikes in remote parts of the world? Can they offer suggestions?
I hope that your sister will have a safe and successful hike.
Skylander