Hi Christine
I am under 5'2 so i understand the difficulty trying to find a small enough bike...
i race on mtb, and standover height is pretty darn important, since inevitably, you WILL fall when you mtb...(Ouch!) in some cases you need to be able to quickly put your feet on the ground, and you may not have the luxury of coming to a nice rolling stop and prepare yourself.
if you are doing light recreational riding on paved paths you are probably a bit safer, but keep in mind that if you need to stop suddenly and put your feet down, you may hurt yourself.
personally i would go for the bike that is the proper fit, since i DO have the proper stand over height and i know what it feels like to land on the frame (did i say ouch )