having just had to load 2 unhandled 2 year olds this evening in driving wind and rain, I can really sypmathise with anyone struggling to load. The method we used (bearing in mind the ponies aren't trained to lead yet and are colts too) was to follow Intelligent Horsemanship concepts. Pressure and release works wonderfully well as it's something horses naturally understand. Of course bribery with food and the use of a lunge line down the sides of the lorry helped enormously too. Richard Maxwell is well known too for his use of a pressure halter to load horses, and having seen it used on several horses, this too might be worth investigating.  The pressure halter is perhaps the gentlest method I've seen thus far... In my humble opinion clicker training has its place but it has to be trained to instil the concept in a horse first, whereas pressure and release is something they automatically understand... 

try putting some used bedding(not dirty stuff) in the trailor keep it light and a haynet at the back, that way the place is alot more iviting becasue it smells like her and thers food for when she gets ther, put her on a lunge line so youve got plenty of space if anything goes wrong, and just spend time with her near the ramp, dont aim to get her in the trailer aim for positive movement towards the trailer at first, then aim to step on the ramp keep her ther and give her lots of fuss and attention do this over a few weeks then lead her up into the trailor and give her loads of fuss again give her some food even groom her in the trailer the more she assosiates the trailor with good happy things the more willing she will be to go in :) just take it one step at a time and if she panics take a step back and try again.