The 911 call will certainly help her case.
It may be more harmful than it initially appears.
Beneficial for her:
She called 911. Apparently right away. She didn't try to hide anything.
It reinforces that she really believed she was in her own apartment. She has to hold on to give the apartment number. You can hear in her voice when she says the apartment number the second time that she realizes that she is in the apartment immediately below hers. She says over and over again that she thought she was in her apartment. She thought she parked on the third floor. Near the end of the call she is obviously trying to figure out how her key opened the door if it wasn't her apartment.
At the end she says that she is so tired, supporting suspicions that it was exhaustion that caused her to miss otherwise noticeable details that resulted in her going to the wrong apartment.
She's distraught. She's remorseful. She keeps saying she is sorry.
The call appears to support her claim that she was attempting to render aid.
Unfavorable for her:
She doesn't says that the gun went off accidentally. She has never publicly made that claim and I don't think anyone believes that was the case, but the call would probably take that claim fully out of the picture.
She seems more concerned with how this will affect her than the man she shot. She keeps saying "I'm" ******, "I'm" going to lose my job, "I'm" done. She seems more sorry for herself than her victim.
Most important is what she didn't say. Although she says over and over and over that she thought she was in her apartment, she never says anything about why she actually shot him. She doesn't say that she thought he had a gun or that he was reaching for a weapon or that he was coming at her or even that the was not obeying commands. She gives no reason why deadly force would have been justified. She repeatedly says she thought she was in her apartment, which is her mind racing trying to "justify" or "explain" why this occurred. If Jean had done something that would have justified lethal force, we would expect that Guyger would have mentioned that while rationalizing her actions during the call. She did not.