A 14.1 H 5 year old QH that's broke, has a sweet disposition and isn't fugly or has serious confo problems is likely worth the initial investment and the time it will take to finish her.
She needs some love, care, groceries and elbow grease. And I'm curious as to why she looks so much better in the photo with Western tack. In the photo, she has nice hunter style movement. Clean her up and sharpen up her front end and you'll have a nice local hunter pony.
QH large ponies are *wonderful* but tend not to be as competitive in the rated divisions against the fancy, typey ponies. Good large ponies that are kid safe, however, are very hard to find, local quality or A quality, and it's the one area of the market that's still a seller's market.
If you can put the mileage on her cheaply, I say she's a great opportunity and go ahead and snap her up. If I still had a lesson barn and a way to put mileage on her cheaply, I'd snap her up. (I have a made QH pony geldin of similar type, and I won't part for him for 10K - he's just too darn useful.) Honestly, you could turn her around as a kid's pleasure pony in six months for $1500 - $2500.
Assuming sound and sane, you can't go wrong.