Well, from the info you supplied on the computers in question I can only conclude that Apple made the MB much nicer than the MBP.
Seriously there are a ton of reasons that yours could start slower, from the hardware configuration to the software.
Have you let OSX run its maintenance programs lately? Do you have menu extras? Lots of icons on the desktop? Is your HD fuller than hers? Define the not big things you have in log in items, just because they are small doesn't mean they start quickly, plus there are several other places OSX can keep startup items.