Thanos doesn't dictate to death.Actually, she's kinda both.
I think they are one in the same in this universe.
Thanos probably told her to go snatch up the Tessaract, she was much more greedy being her ex-home and had some fun with it.
Loki grabs it, will give it to Thanos, and Hella ain't dead, so...
Hella is most powerful on Asgard, but still squeezes Mjolnir into exploding with one hand stating, "You have no idea what I'm capable of".
I'm thinking it's 50/50 at this point.
I agree with the thinking that Hela and Thanos' Death are two separate things. Thanos goal (in the comics anyway, hasn't really been explained in the movies yet) is to win Death's love. Death is upset that there are more beings living today then have ever died, to fix this imbalance, Thanos wants to kill off half the universe.