This is a website and it is public but your identity is private to all but the owner and administrators of this board.
As soon as I read that, I realized that others DO have her identity. Plus, if she has ever given out her ebay sellers name, her contact info can be pulled. By mentioning what she sold and for how much, doing a simple search will bring her right up on eBay....especially when some are posting what days their aucitons ended..and other info. I have found several people that way from this board myself. While you may not think the IRS would monitor this board, you really don't know that for a fact. We really don't know who is here. Giving out income (especially unreported income if it is..not that I'm saying it is, believe me) on a thread that is being read by so many is never a good idea, even if it is just meant to encourage others.
Unless we actually have an IRS person that can attest to the advice you have given, I would still recommend that people not give income.
Some of my tax clients have been reported by neighbors and friends, and ended up with a very close scrutiny of their taxes. Working with enrolled agents, that have defended my clients, I'm never surprised anymore how the IRS gets private info. If your relatives that work for the IRS were to agree to come on the thread and guarantee that giving out income on a public board is a fine and a good idea, and that no one could ever get her identity, then I would be very surprised. eBay itself says they are just a venue and their records are wide open to the IRS.
It's one thing to say you could make enough money to go to Disney..it's quite another to give figures. Not only should that IMO be personal info, but not everyone has vintage Barbie Dolls to sell, and it actually may make some people decide that they could never meet their goal by selling "stuff around the house".
As an aside..I gave out my eBay name on this very board, and had to go back to erase it from all the messages, because of something that happened to me, as a direct result of posting on this board. So you just never know who is here reading.
I stand firmly by what I wrote earlier.