One could argue that Clytemnestra is not justified in killing Agamemnon and is therefore not a martyr, because her murderous act does not end the cycle of violence which included the death of her daughter Iphigenia.
Clytemnestra is certainly entitled to feel hatred towards her husband for sacrificing the life of their daughter. One can even sympathize with her desire for vengeance. But as the saying goes, violence only begets violence, and that's what happens when Clytemnestra's son Orestes gains revenge by murdering both Clytemnestra and her lover, Aegisthus, in the next play in The Oresteia, The Libation Bearers.
Clytemnestra's murder of Agamemnon is all the more difficult to justify given that there are mixed motives at work. As well as being motivated by revenge for Iphigenia's sacrifice, Clytemnestra also wants Agamemnon out of the way so she can be with Aegisthus, hardly a noble motive one might think.
And with Agamemnon dead, Clytemnestra will now become more powerful. It's difficult to see, therefore, how her murderous actions were not, in part at least, motivated by excessive pride.