Faye told Bubbles that she didn't need to wear the outer plating because, even without it, she couldn't be damaged by anything other than a high-power rifle. That was when Bubbles indicated that her armour wasn't about protecting herself from physical injury.
When Faye asked about her armour, she said "Why wear it then? Anti-tank rifles are illegal in this state." That did not imply anything about what she thought concerning the protective nature of Bubbles' skin. It only implied that wearing armour is unnecessary, since people aren't carrying military-grade armour-piercing weapons around on the street.
And FWIW, an anti-tank rifle is
a lot larger, heavier, and more powerful than a .308 magnum. A .308 would penetrate Kevlar, but not your average body armour. Some of the ones used in WWII fired a smaller bullet (7.62mm), but with more power, and hence a higher velocity (they also had a tendency to injure the person firing them, because the recoil was so strong), but they were only effective against light armour. With the thicker armour used on tanks in the latter part of WWII, those rifles became essentially obsolete, since they were no longer effective against tanks, but were too heavy and powerful to carry as a regular small arm. Even the British "Boys" .55 caliber anti-armour rifle became largely ineffective by the end of WWII. The Browning M2 .50 caliber machine gun is still effective against light armoured vehicles, but at 121 lbs, it is far too heavy to be carried and must be mounted on a vehicle (or in an aircraft). Even the "light barrel" version weighs 60 lbs without any ammunition.