Is there anyway to get Medresi Dran back if I've killed her? I want to finish her quest. I am playing on PS3 so I cannot use console commands.
Since you're playing on PS3, you cannot resurrect her with console commands, so the only way to bring her back would be to reload a previous save from before her death. However, this isn't necessary, as her questline involves her death regardless of what you choose to do.
Since you haven't mentioned which quest you are talking about, I'll answer for all of her related quests.
If you were talking about Medresi Dran and the Wandering Dead, then based on the information on Medresi Dran's wikia page, it looks like she was supposed to die regardless of whether you chose to help her or not.
If the Dragonborn agrees to help her, Medresi will still die. After opening the gates, she will run forth greedily to find the treasure herself where she triggers a trap that impales her with spikes.
In fact, even if you are able to save her from being impaled, her fate seems to be sealed:
Although it is possible to save her from being impaled by the trap, she will still die afterwards.
No matter whether you kill her or she is killed by the traps, it shouldn't prevent you from advancing in this quest.
You may have been referring to the quest Destroy the Draugr in Angurvunde. If this is the case and you have indeed killed Medresi Dran, then the key required to progress the quest can be looted off of her corpse, which will then start the quest Discover the Treasure of Angarvunde.
tl;dr: She's supposed to die no matter what, so killing her prematurely shouldn't hinder you in any way. She doesn't need to be alive to complete her related quests.