I didn't read any of the responses, so here goes:
The pony's showing at Upperville, so it has to be good. Its form is good, and considering she placed second says something as well. She's very careful over the fences and isn't rushy. She's showing 3', which is in high demand for ponies. Depending on the age and hieght, I'd say she's worth anywhere from $30,000 (for ~5-14 years of age) to $15,000 for an older mare.
Ponies like her are in very high demand - she's fancy and very cute over a hunter course.