KillarneyRose,
Can you provide a link that shows the watch you are talking about? I haven't seen it yet. Judging from your descripion, I think I agree with your sister. Of course you shouldn't let someone else's opinion dissuade you from getting what you want.
That aquamarine watch is beautiful. But I wouldn't be able to justify the cost.
I usually wear a watch that looks similar to this one:
http://shop.store.yahoo.com/miamiwatch/ny3007.html