if you just want it to look cool and your obviously a chic so paint it pink with some decal get pink under glow and get some sweet rims (you can get some rims that are pink if you want a really pink car) and if your into loud music that kicks a bit put some subs in that would be pretty kick ass for a chick i think for the inside just get a stereo that looks cool but maybe get some seat covers and a steering wheel cover
Personally I wouldn't even bother - would be such a shame to ruin a new car with shoddy workmanship.
If you really wanted I would find a car electronics shop and ask him for suggestions - look for a busy one! Also remember to ask him\her to confirm the cabling, etc will be clean and that he wouldn't be creaating holes in the car!