buying a car from a relative can be a win/win or a problem. you need to talk to them ahead of time and agree that there are no hard feelings if you buy it and the next day the motor blows up.... you need to at least talk about it..
when you buy from a stranger, you buy it and that's it.. but when you buy a car from family - some people can wind up with bad blood over $$ issues or repair problems. as long as this is all worked out and discussed in advance it can be a great deal.
i shoudl know, I bought my boxster from my dad. i knew the history, which was good..and he wanted to unload it. we worked out a fair price, and it was a true win win. i still let him borrow it from time to time... everyone is happy.
that being said - you may want to test driv eother ones. there are "S" models with more power, better brakes..newer ones with glass windows, etc etc..
if you are getting a great "family" deal..it might be the best buy out there. if she is selling it to you for "full retail"... you would likely be better off finding the "perfect" boxster - that is exactly what you want, and just ge ta really good PPI done to ensure nothing is wrong with it.
good luck.
the boxster is a blast to drive. whatever one you get - as long as you get a good one - you'll be VERY happy.
nothign is quite like a great drive in teh box on a nice day with the top down.