What would be a better hobby to earn extra income?  

Both will require an upfront cost for supplies so I would say whichever one is cheaper to start. I would imagine that soap-making costs more as you need to get a bunch of tools, molds, etc. as well as specialty chemicals. Wax is easier to come to buy and cheap in bulk. The heavy part of the cost will be fragrances and jars. 

I agree with the post above. Both will cost money so it is best to go with whatever would be cheaper upfront. I think you can earn more per candle as well so that is something to consider. If you are just making bars of soap, compare the cost of them to chain and handmade ones online. 

I don't think either of these will earn decent unless you already have some sort of following on social media. It is hard to earn money online without something like this when it comes to creative skills. Sad but true. 

As mentioned, it is going to cost up front and there is no guarantee of sales. 

I would personally look into other options. Maybe making use of items she already has? I heard people make good money upcycling used items.