She's very pretty. I can't really tell from your photos, but she might have a slight divet running down her backbone?
I've spent 4 years trying to figure out overweight minis, feeding regimes, etc. and still don't have it figured out entirely.
What I can tell you is:
--You're not going to see any significant weight reduction in 4 days. Four months is more likely.
--Vets... I understand the expense involved; unless you have a weight related problem, it's probably not necessary. I wouldn't spend just to get a weight. But it would make your life easier if you could weigh her or at least estimate her weight with measurements. That would give you a baseline, and you could continue to measure over a period of time (like 6 months to a year) to see if there's a decrease in heart girth. Also... there's body condition scores. But I've had two different vets give me different visual scoring on the same horse within six months. Most of the stuff you see on body condition scores is accompanied by line drawings that make little sense to me. Here's a link where they show photos with the scoring. It's somewhat more helpful, except the photos are full-sized horses; ponies/minis are built differently:
http://www.admani.com/horse/Equine%20Library/PDFs/S9748D%20Equine%20body%20codition%20scoring.pdf
--Weigh your hay; flakes (biscuits) can be many different sizes in the same bale.
After our filly had laminitis, the vet instructed weighing out grass hay only, soaked/drained to remove sugars. No slivers of carrots, no Dr. Dobbs apple treats, no grains (bagged feed, which here in the US are drenched in sugary molasses.) Absolutely no alfalfa (lucerne.)
--My farrier is my "weight tape." He's a man of few words; in the early days he used to run his eyes down their bodies; then he'd feel the crest of the neck; I'd either get a nod or that one raised eyebrow (which meant I was doing bad on the food front.) Since then I had him teach me how to feel the crest. I couldn't even begin to explain because there's a difference between fat and muscle, but for me grabbing the neck and giving it a squeeze is the easiest way for me to determine.
--In regards to jumping, go with your gut feeling; if impact sounds bad, maybe it is--maybe it's not? But how much do you love her and if you don't know, are a few jumps worth the risk?
