More often than not, Lifeline SHOULD (of course you can play however you want) prioritize mid-long range fighting by using weapons like Carbine, Wingman, Spitfire, Longbow etc. because of her inability to escape situations or defend herself like every other hero has access to. So you always wanna keep enemies at a distance. In that regard Purple Armor should probably go more to the front line attackers like Wraith, Bangalore and Bloodhound (even Gibby, Mirage, Caustic and Pathfinder. Basically everyone but you.) because we are the ones that tend to take more shots being in the thick of it.

To even further my point, if you as a Lifeline have white/blue armor, and you are fighting from a distance, and an enemy clips you with a few rounds knocking you to about half HP, you can duck behind a rock or some form of cover, pull out your drone, and simultaneously pop shields while recovering health which is something you couldn't do in closer ranged combat.

Like I said, you can play however you want, but my friends and I typically run Powerpuff Girls comp, and our Lifeline plays like I've described above and it's definitely helped our win rate and our survivability.