In reply to tony:
When you enter you have to demonstrate appropriate experience. Quite how the organisers prioritise factors and decide what they are happy with or not I'm less clear on (and wouldn't like to comment), and how you/they 'prove' certain things etc I have no idea.
I am a mountaineer who has started running in last couple of years (having done a marathon on road a few years back). I had a Lakeland 50 in a reasonable time under my belt and 2 or 3 other fell races in the 20 to 30 mile distance on sport ident so my running credentials are provable. Plus to do a 50 mile trailrun (and the others), one has (probably) done a good bit of unsupported long running too. I also stated my climbing/alpine background which is less easy to prove but hopefully (in my case) the wording or way I described myself indicated that I knew what I was up to. For this race (in my opinion) mountain ability is crucial,perhaps more so than simple running... a road runner or ultra runner who hasn't done any real hard fell or mountain races and/or who is not also a mountaineer shouldn't be looking at it.
I don't think it is necessarily vital to have done a similar race (indeed, having never raced outside the UK I would struggle to name anything in this country quite the same, even although Spine and Dragons back etc are seriously serious) - but I think it is vital to prove that you are both a mountaineer and a runner - without a bit of both you would be a liability. Perhaps the race reviews, descriptions, pictures now available may give her a better view of the nature of the race although I thought it looked pretty clearly to be not for those without mountain experience when I looked at it.
Perhaps the best indication is that I was surprised and delighted to obtain a place, and that's with 20 odd years of climbing, alpinism and general mountaineering and a couple of years of proving that I can actually run a long way, on trail and with a lot of ascent thrown in. If I was surprised and delighted, should somebody with little or no mountain experience even be thinking about it?