[sblock=Negabeam]I don't think it's as bad as you're thinking, for several reasons. One, it's a fairly low power effect. At 5 ranks, it takes some luck to shut down even equal-PL tech powers. I'll be raising this as we go, but especially for huge "installation" powers like the shield, you can always just place its power level way beyond Echo's nullification ability.
Two, it's not an area attack, it's targeted. This means Echo can't just hit everything in this area with the Nullify...she has to choose something to shoot it at. Right now, if Echo wanted to try to Nullify the shield, she'd have no idea what to shoot...what's generating it? What specifically, that is? Logic suggests she'd have to find the power center, or some kind of 'shield core' that is directly responsible for creating the shield effect, then aim the Nullify at that.
Three, the weapon is essentially an "EMP cannon," or a High Energy Radio Frequency (HERF) gun. It overloads electronic components by inducing high voltage currents in them via electromagnetic induction. You are within your rights to designate certain (especially plot-critical) items of technology as hardened against such attacks, or using high tech components that are not vulnerable to EMP (such as optical electronics, or encased in a Faraday cage). And of course, items that don't use electronics (like your average handgun) wouldn't be vulnerable anyway.
Fourth, only powers can be Nullified. A giant robot could not be completely shut down by this power, because a giant robot is not a power. It's a construct. Now, the Nullify could, on a lucky, lucky roll, screw the giant robot up a bit by shutting down all of its powers...but remember that this only affects powers that are ongoing, because it can simply reactivate them again. The Nullify can't stop its guns from working, because the guns weren't on when the Nullify hit. The only exception to that would be if the Nullify is used as a Counter, and fired at the same instant the gun is fired.
As far as game mechanics go, the Nullify is an instant effect that, if successful, shuts off all technological (electronic) powers that the target currently has active. Those powers can be restarted again on the target's next turn with the appropriate action...which in some cases will be a standard action, but in other cases may be free. In the case of the sensor dome, for example, the sensors...all of them...would turn off if the Nullify is successful. But the operator could simply reset them, turning them back on. It doesn't actually do damage to the system. Though in hindsight linking it to a limited damage effect would have been an excellent idea.
Does that help?
Don't get me wrong...it's still a very handy little tool. And with experience, she could improve it in any number of ways. But I don't think it's in any way a plot buster.[/sblock]