Overall pretty well done - very impressive on the first glance, and gave my standing "best Rainbow Dash" choice a bit of a fight. It's not perfect - nitpicking to follow - but it's got a lot of potential.
I'm going to start by saying the tail is excellent, nothing that really needs to be changed or fixed there.
Body's good, but maybe just a little long? Consider taking a bit out of the section between the front and back legs - not much, probably somewhere between a half and a whole inch.
Wings are well done too, not much of value I can say about those. Cutie mark's great, I really like the eyes - you've definitely got the embroidered parts down.
The back legs are a bit weird. You might want to look at making them a bit more narrow at the top, tapering down to the weight you've got now for the hooves. As it is, the top of the leg just feels like it sticks out a little far behind the hip. It also feels like it's got a bit more of a point to it than it should, but that could just be my imagination.
Front legs are fine, well spaced and shaped.
I'm personally a fan of narrower faces, but it doesn't make wider ones wrong, so I should refrain from commenting on that; what you've got works for the style it's going for. Nose is shaped well, you've hit a good length for the snout, which is something people don't always manage; good job there.
Mane over her shoulder is good, but over her head, it feels like it's got a bit too much volume; you might do well with a little less stuffing there, though you'll still want a little, I think.
Now, this feels a little petty of me, but... the forelock should be yellow/orange/red, without repeats; the yellow/orange/red/orange/yellow setup you've got loses points for accuracy, but you can call artistic license on it.
Ultimately, I think you've done pretty well here. If it's sounded like I'm being a little harsh, it's because I'm looking at how this compares with top-grade plushies - and you're sitting at only a few tweaks away from fitting right in with them.
Actually looking at it.. I think the body length is perfect. My arm fits nicely under her tummy for carrying and hugging. The embroidered parts are perfect. The rear legs are not as bad as they look in the photo. The chosen angle of the picture is pretty much worst case and the black background does not really help. Still, they could stand to be a little narrower or her flank a little fatter. The Mane is an excellent idea on the top of her head, however it needs a little bit of reengineering. Its seems to prefer to lay backwards between her wings. I think putting a couple stitches on the biggest section of the red piece, straight through the orange piece to the top center of her head, would fix this while keeping the colors separate as they are. There are probably other ways, this is just one I thought of that wouldn't take much time or modification to the design.
Have you ever considered making another Dashie? Your ponies have improved tremendously since this one. The forelock is a very interesting take on hers by the way. Looking back, would you keep this style and improve it, or just totally remake it?
I live in LA, so I can go down to the fashion district and get my stuff. But you can buy most of what you need at any fabric/craft store. However, if you don't have access to specialized minky stores like I do, your best bet to finding good quality minky is online.