I was like this as a child. Please don't refer to her nervousness as being "over silly little things", I completely understand your frustration, but my DM did this and it just made me worse because I then got worried than everyone thought I was being silly and it fed the self-doubt and anxiety.
I know how frustrating it can be, but it probably is for her, too. If she's happy just hacking, can she not just do that for a bit? I'd offer Pony Club, but be aware that it could make things worse by adding pressure - I found Pony Club quite overwhelming when I was very nervous, and there were lots of very brave kids doing things I wouldn't dream of, which fed into the insecurities I had.
Eventually, I stopped doing the things that made me nervous and just did a bit of intro and prelim level dressage, lots of hacking and fun rides (which I did jump and canter on) and that was it for several years. When I moved onto horses something "clicked" and it was actually having the autonomy to pick what I wanted to do for myself, plus learning how to really "ride" my sensitive TB (previously I'd just bobbed about on ponies) that got me my confidence. Since then, I've brought on youngsters and several ex-racehorses, hunted, evented, and I'm generally pretty brave, although I do still get the odd bout of nerves before a XC round. I wouldn't have got there by being pressured, though, it was only really a good, patient instructor with an excellent understanding of riding psychology, and my parents taking their feet off the gas with it that allowed me to find my own way. I also learned that being brave isn't everything. I may not be the bravest rider, even now, but I'm quiet and kind and sensitive horses go well for me and I can get a good tune out of them, which is a great boost. I'm not the right rider for the strong, ballsy hunter that wants to be right up front, but I am for the ex-racehorse that needs some patience and understanding. I never got on with ponies, and, to this day, I feel safer on a horse with more in front of me.