From what I have seen on completed auctions on Ebay, looks like she has a wide range between $10 and $25 US. A couple years ago I got mine off Ebay for $6 plus shipping. Just depends I guess.
How are you selling her? US/Canada ebay euro/uk exclusive ponies sell far higher then they tend to on UK ebay. So if you list her on ebay, you'll likely do well. On the forums roughly $15- $20. She's one I need to get someday, I have all her accessories- but no pony!