Is a 5'4 - 5'5 girl too tall for a 14.2 Arabian gelding?

As long as you and the horse are balanced then there is nothing to worry about. I have ridden a 13 hand pony a couple times at shows and we have always come in first. You just want to keep it nice and balanced and flowy. But also with an Arabian their backs are one of the hardiest things on the planet.