I've gotten 8 heroes through cosmic trial and She-Hulk has been the easiest by far (though part of that might be the synergies I have that I didn't before). I built her up with decent health and defense.
I love her combo system. With Punishing Verdict talent at level 44 and Always Another Case at 56, you can pretty much spam all your heavy hitting attacks constantly.
Long rotation I used was:
Opening statement -> Assault (build combo points to 5) -> Barrister Beatdown (sometimes) -> Final Verdict -> Objection -> Move to Strike -> Conviction
Short rotation was just the first 3 moves.
I used the Gorgon medallion since she can use her signature so often.
"You're already dead." -Psylocke (probably)