First off - the modern day Irish Draft isn't in any way comparable to the type of cart horse draft type - they've been bred to be riding horses for years now and make excellent hunting and showjumping horses. They never were your typical heavy farm horse and the original ID's were much smaller than they are now as Clydesdale was crossed into them to make a bigger heavier type - it was a disaster and has been bred out of them over the years.
The Hanoverian breed also make good showjumpers so its a good cross
I see no reason why she shouldn't do well - she just needs more schooling and a lot of fitness work to get her there
I'm about your height and competed on a 17.2 Irish Draft x TB for a long time with no trouble at all - getting on is the hardest part and getting them used to having a rider who's legs are only part way up their sides - that wasn't a problem for me as I broke the horse so it was all he was used too and this one looks to be ridden by a small person too
Can a real draft cross jump at top level - the UK's Ryans Son was a Shire x TB and managed it for many years even with his signature bucking as he went round - and he was only 15.2 https://www.youtube.com/watch?v=d0MgS0z-mTc https://www.youtube.com/watch?v=WPcY54HZw0Y