As a 16 yo maiden, I would expect her to take several times of AI to catch. She may or may not settle because at her age she may not produce enough of the hormones to make the embryo 'stick'. She's also more likely to have a 'dummy' foal and that comes with its own set of issues, near term and far reaching. My rule of thumb is pretty much 13 years old as the oldest maiden I'd breed. She could catch on the first time with live cover, but retention could still be an issue. I'd have to be in the 'buy a foal' camp. I'm sure she's pretty, but do you even know her pedigree? Her 5 panel status? There are a LOT of reasons why I would not breed and very few for why I would.