The diploma regulations, which I'm sure you've read and know rather better than I do (as my diploma is from Trinity not the AB

), state that you should choose a
general programme that covers wide range of styles, moods, periods etc. Think of it as being a chance to demonstrate as many different aspects of singing as you can.
As you say, you will have to choose a number of works, and you're not allowed to have any two by the same composer, so you're going to be able to choose a good variety of material.
Choosing mine, I had a mental list: had I covered the main genres - Baroque, Classical, Romantic, Modern? Had I incorporated opera and oratorio rather than just songs? Had I demonstrated recitative, coloratura techniques, lyric singing? Had I shown my full vocal range? How many languages? At a rough estimate 35 minutes is about 9 items, so there's a fair bit of leeway.
Obviously you don't want to sing anything that really doesn't suit your voice, but you are going to have to sing outside your comfort zone to some degree - and you may surprise yourself! For example I'd always preferred the late baroque/early classical music I'd sung, but I discovered a real enjoyment of the modern composers in my repertoire and my LTCL choices so far are based on this discovery.
I'd also suggest you collect your songs first, and don't worry about performance order up front. An order may well suggest itself to you as you become more familiar with the works. I discovered that my "start" song and "finish" song were obvious from early on, but some of the middle order needed a fundamental re-work as I ended up with two strenuous works (a Romantic song by Berlioz and an aria by Mozart) together, leaving me without the resources to move comfortably to the next item.
Good luck with your choices - part of the fun is trying out the repertoire in the syllabus before you make your final selection. Enjoy!
Cheers
Katyjay