Yes. が works as 指定の"が" (が for specifying) there, i.e., it emphasizes that the person who tried to kill was 父, not anyone else. Also, は can be the contrastive marker depending on the context.
Other than that, is your father already mentioned previously? Plus, is the narrative written from your view point? You also need to pay attention to a fact that 父 could be misinterpreted as "her father" depending on these factors.
In conclusion, all those things, whether the object can be omitted or not or which should be used が or は, totally depend on the context after all. Can you show us the previous sentences?