As for specs, yes, the stock S2000 has more hp but it also weighs a little over 300 lbs more. For about $1000 in upgrades, the MSM can easily match the S2k.
She really should drive the S2K though. It is a very different car so it all depends on what does it for her. Numbers aside, they do feel different and one may suit her better than the other.
(there are dyno charts up on Flyin Miata's website. A stock S2K had 206 rwhp and 138.2 tq. The MSM with just a few upgrades was 203.4rwhp and 194.6 tq. A lot of people have done the mods they used on that dyno run with a couple of other small things and hit 210 or 215. Of course there are additional upgrades that took the MSM to 270rwhp.) http://www.flyinmiata.com/tech/dyno.asp