Most eBayers who sell for others, get a little more than what you mentioned. eBay is a lot of work. Be sure to decide who will pay the fees (if it sells or doesn't), and who is reponsible for packing and shipping. It's your feedback!
eBay is a venue only. They do not keep track for you of your profits, etc. However, they do open their records freely to the IRS, and they will tell you that, if you ask. If you don't want to claim the income, I would suggest you have your friend set up her own eBay account, and you sell from there. Keep track of your expenses, since your income from her is traxable income. You might want to set up a schedule C, for self employment, so you can take off your expenses. Otherwise, this would go on your income tax as misc income..but then you can't take off your expenses, so your tax would be higher.
While the IRS doesn't often bother the "garage sale" seller (not saying they never do, because sometimes they do), they certainly have gotten interested in the amoutns you are talking about. Keep in mind, that although the IRS usually only goes back 7 years, if you have an IRS problem...in the cases of fraud (withholding income) they can go back forever.
I would not sell something (just my own opinion) of that value on Yahoo...they just don't have the buyers at this time (their counts are wayyy down), and you would still have the same IRS rules to follow.
Just as a PS, eBay has just raised the prices (not in effect yet) to put items up at a reserve..be sure you check your new fee schedule before setting unrealistic reserves..you pay if it doesn't sell for at least your reserve. If your friend sets all the prices too high, and you are working on commison, you will be doing a lot of work for nothing.
Good luck in this venture!