Yeah that's not a bad deal at all.
The Margay is most likely a converted Sprint kart that was originally intended for racing on paved road courses with right and left turns. It'd be fine for the kid to start out with but would be at a disadvantage and not handle/turn as well as newer Offset chassis that were designed for oval racing.
That 2003 Trick probably is an offset chassis specially designed and built for oval racing. If you want your kid to have the best chance of doing well, I'd let her race this chassis. You'll find guys at your track that'll have nice used/small race seats for sale for like $10 or $20. Some of these seats would have originally cost $100 and they'd work just fine.
This link list several kart tracks in your area:
http://www.na-motorsports.com/Tracks/FL/#OutdoorKartTracks
You'll probably find many of these tracks have web sites with classified sections you could search for other karts for sale. Those web sites might also have the rules posted. At some tracks, the beginner's have to race in the clone-engine classes. So If that the case you should plan on having to spend more money on engines.
This link has several used oval racekarts for sale so you could compare pricing:
http://karting.4cycle.com/forumdisplay.php?f=55
(just like cars, the year makes a huge diference in pricing...)
You'll also find this whole forum:
http://karting.4cycle.com/index.php? will be your best source of on-line info for oval kart racing in general.
I race dirt oval karts out here in Arizona, I'd be happy to answer any questions you might have. You'll find a lot of info/pics in my thread here:
http://www.diygokarts.com/vb/showthread.php?t=6364
