I bought a (relatively high end) Janome sewing machine from a local dealer a few months ago, before that I was looking around in the second hand market a bit.

If the unit OP was selling was around me at the time, I'd had bought it for such a low price and good quality.  OP's original sale included the buttonhole foot and a overedge foot, these alone are already quite rare. As most used sewing machine sellers absolutely don't include anything at all, many do not even test the machines. The very same model is still being sold for $325 untested by someone.

What the buyer missed are maybe the zipper foot and a few other things. They were not included in the original listing, so I don't know what makes her think she can simply demand.  She can either buy a generic replacement, or a genuine one from Janome, or the lot from OP for discounted prices.

Of course if buyer want to enjoy unboxing and count all the parts / presser feet / bobbins / thread cutter / free scissors, watch manual on a DVD player, she can spend a thousand dollars for a brand new one, like I did.