As far as what to worm her with, I think I'd ask the vet. Your vet would know what is best for your area. I am in southern Middle Tennessee and we barely had a winter. I wormed my four with Equimax.
The pic below is my Generator-bred fella, I mentioned above. He's full of sass and attitude, so I was using him to demonstrate how to make a halter in less than 30 seconds with a binder twine.
This was in 2011 when Rusty was 17. He was at a pretty good weight yet you can still see his hip bones. It's safe to say, at 17, those high hips aren't going to disappear- lol He topped out at 16.1H; he's been with me since he was 2-1/2.
He is also a very narrow chested horse by nature but he is a powerhouse of a horse. When I hear thunder coming down off the ridge, 1,500 feet away, I know it's him. My Equine chiro's husband trains QH's and they were both impressed with his natural muscling.
I am thinking your Filly might have Generator breeding or Pusher or both, just by her build. I've been known to be wrong before, however - lol
I just wanted you to see my Generator "hippy guy" with the narrow chest, so you won't be disheartened. I've had this horse on trails so narrow and steep-sided, there was no way to turn around. He instinctively knew what to do and it's a good thing because I had my non-horse husband on him before we were married - lol lol lol That was pretty much his last ride lollollol