Can the new Saturn Girl be used as a Brilliant Tactician (usiung her special power as the perplex component) ?

I don't believe that a power granted by a Special Power can be used to meet the prerequisites for a feat.

I suspected that thanks:knockedou

This is correct.
Besides, even if Special Powers did count, Saturn Girl's special power doesn't have anything to do with Perplex - nothing in the power description says it is Perplex. It has a similar effect (offering stat bonuses), but if that's all you go after you may as well let figures with Phasing use Pounce as Phasing is kinda like Leap/Climb...

Point taken - true enough

Hey, about the same saturn girl... what its the point of having the ability to rise a friendly character defense value if this bonus goes away at the end of the turn?

There are sometimes instances when your characters may be attacked during your turn. For example, if you are hitting an opposing character with EE and one of your own character would be with the splash zone, increasing its DV may protect it. Also, characters like the Scenario version of Galactus do not have a turn of thier own. Instead, they retaliate when you attack them (during your turn). If character A is going to attack Galactus, Saturn Girl can use her SP on A's DV to maybe make it a bit more likely that Galactus may miss.

Ok thanks!