Hi Saphy!
Looking at ebay sold listings she seems to be just above the usual price, at around 5-6 loose, and 9.50 complete (card and brush). However, she has marker on so I would put her at 4-6, depending on how visible it is
Ponies that are worth more than average are:
Holiday ponies - usually it's having them with accessories that pushes their price up, as they are so cute!
The winter babies (Northern lights and winter ice) and Mejers exclusive babies (ribbons and bows and jingle jangle). Again, accessories will make their price higher.
The birthflowers. These are very popular, and I'd say $10-15 on them.
Jewel birthdays - not worth too much more than regular ponies, but a little bit higher.
Beach belle and Caribbean delight - the last pair to sell that I know of went for £63 ($85) they were mint and complete.
Fair/comic con/UKPonycon pony project ponies - some are worth more than others, but definitely over regular prices.
Tink a tink a too in Sweetberry's pose very sought after and HTF
Sweetberry in minty's pose (just as HTF, but not very sought after),
Winter Snow
Snowdrop Swirl and Rainbow Bubbles
Whew! Sorry for the lengthy post, that's all the ones I can think of right now
Also, in the UK not many of the US target and other store exclusives came here, so like g1s, they seem to have more value in places that they weren't available
I'm sure I have missed some, so hopefully others can help fill in the other ponies
I apologise again for the long post, but I hope it's useful for you
Mlp Sunsparkle x