I never played the first Spec Ops so I don't know if we get some every week or not. You can request it as a gift from allies and I hear you can buy it too but I don't know if it's from stores or they mean buy it real money. You can also get it as drops from enemies and as rewards from certain fights.
As for Emma, I doubt it, as like any other AI character that the game sometimes forces you to fight with, they always base their power around your Agent's level so they don't die seconds after a fight.
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The mass chunk of iso's you get at the beginning is a one-time thing: use them wisely.
Best way to get more is to use your daily limit of 50 gifts only for iso's, if you don't feel like spending any money.
Protip: the objectives you have to do for Emma (like finish 1 deploy, use X-Men in battle) don't need to be used in Spec Ops. Don't do deploys and such if you don't have to for the objectives; fight only bosses and high threat enemies.