I have a pup that was nervous of other dogs due to a combination of lack of socialisation (he was very ill as a young pup) and being leaped on by out of control dogs when he was first allowed out.
We went to a great puppy training class, where the trainer set us up with quite a large area and instructed the other owners to stay outside of our 'zone'. The first week he didn't want to come out from behind my chair and hid behind a curtain. I threw him a treat every time he looked into the room or at another dog or took a step forward, by the end of the lesson he was watching the class from behind the chair. Second class he hid for about 5 minutes, then gradually crept out (being rewarded for every step forward) and by the end of the lesson way lying in front of me watching the class with me dropping treats for him calmly watching the other pups. Third week he joined in the exercises and by the end of the six week course was actively taking a step towards some of the less boisterous pups and wanting to say hello.
After the second round of classes he was happy not to have his own zone, would queue up with the others for recall exercises. He even had a girlfriend
and was playbowing at other dogs and saying hello nicely. The classes were vital for allowing him to feel safe and gradually develop confidence to want to interact with the other dogs. He wasn't forced at any point and only ever introduced to dogs he actively approached of his own accord.
While this was going on we avoided close introductions out and about where the parameters where difficult to control and only let him interact with known, friendly, well socialised dogs and only if he showed signs of wanting to.
One thing I did teach him that really helped was to give into lead pressure - ie the 'lets' go'. A tight lead can make them feel trapped and more likely to react and I needed him to be happy to come with me if a dog I didn't feel he should meet approached and didn't want tightening of the lead to cause him to react. Kikopup has a couple of good videos on this on YouTube, and . This really helps with the 1-2-3 rule, as it means you can remove your dogs from the situation, without them responding negatively to lead pressure.
My boy is now 1 year old and fine saying hi to on-lead dogs, but occasionally still panics if approached by off-lead dogs when he is on-lead. The trick was going at his pace, taking his lead and never pushing him to interact with other dogs. We don't approach or say hi to every dog we see and I still judge whether or not to based on the other dog's behaviour and my boy's own body language. If he seems keen and the other dog appears calm and friendly I usually speak to the owner first, then allow an introduction if it's ok, if he looks at all anxious or the other dog looks over-excitable or it's body language is tight or jerky, we just use the 'lets go' and give it a wide berth. Certain dogs we know and I can decide to completely avoid them from the other side of the park/field. The other week we went on a behavioural workshop and he had a blast charging around an indoor riding school with other dogs, I was so pleased, as even a few months ago it didn't feel like it was ever going to happen.
You sound very sensible and committed. Good luck with the classes and I hope it doesn't take long for her to realise other dogs are, usually, fun to be around. 