Why was she allowed to do Deadpool?

Because those DC series she's been in is not even in the DCCU. If she were cast in BvS and its connected films then there may be a non-compete.

DC wasn't worried??

Plus DC is going to be a great multiverse.

All good.

Why would DC have anything to say about that?

The Screen Actor Guild would come after Warners with everything they got...which in terms of legal fire is considerable...if Warners tried to enforce a "non competition " clause.
And I don't think DC/Warners really cares that much,to be honest.

Really? How short are your memories, ADHD Generation? Ryan Reynolds as Green Lantern, Weapon X, Blade's Hannibal King? Question should be "why is Ryan Reynolds allowed to crossover (or do movies period for that matter)?"

Besides, Morena is so so freaking sexy. Definitely on the No Pull Out List.

So Warner can disregard a legal contract? I doubt that. They may be able to buy it out, though.