Cordova was wounded and taken to hospital and her adult son was killed in the attack, the state prosecutor's office said.
The other four journalists killed this year were also targeted while out and about.
"Murderous impunity", ran the headline of an editorial in La Jornada, the national daily for which Valdez worked as Sinaloa correspondent.
Images in Mexican media showed a body lying in a street covered by a blue blanket and surrounded by 12 yellow markers of the kind typically used to flag evidence such as bullet casings.
Valdez was the award-winning founder of Rio Doce on-line news, and author of several books about drug trafficking in Mexico.
On Tuesday, the front pages of the country's major newspapers carried pictures of Valdez as journalists demonstrated in the centre of the capital, Mexico City. No one was hurt. An additional 50 were slain during the same period under circumstances that have not been clarified.
Mexico is considered one of the most risky places in the world to be a journalist.
On Saturday, seven journalists were assaulted and robbed by a mob of about 100 armed men on a highway in the troubled southern state of Guerrero.
Valdez was aware of the dangers of reporting on the drug trade. Experts say Guzman's arrest a year ago and extradition in January have led to upheaval in the area as rival factions war for control of the gang. "You have to assume the task that falls to you as a journalist either that or you play dumb".
"I asked him why he risked his life (for his work) and he replied: 'It is something I like doing, and someone has to do it". "And in that sense, it's a huge loss for everybody". According to the Committee to Protect Journalists (CPJ), at least 40 journalists have been killed in Mexico since 1992 for reasons related to their work.
"As a citizen, I share journalists' and the publics' desire for justice".
Cacho, for her part, said it was essential that the dialogue include reporters based outside of Mexico City and that participants analyze problems such as the scant security that many media outlets provide to their reporters in outlying states.
"Even though you may have bulletproofing and bodyguards, (the gangs) will decide what day they are going to kill you".
"But the state is not capable of investigating properly and that is an inducement for them to keep killing journalists". "This lack of accountability perpetuates a climate of impunity that leaves journalists open to attack". The CPJ reported that, in the weeks before his murder, Valdez told the CPJ that he was concerned for his safety. "That is the federal government's fault".
Numerous media and human rights organisations including Amnesty International have called for an impartial investigation.