Lauren McNamara says 'none of this is private information' while discussing her online conversations with Manning in 2009

A former confidante of the WikiLeaks suspect Bradley Manning has defended her decision to hold an online Q&A about the soldier's forthcoming trial, despite her having been named as a key defence witness.

In an open session on the Reddit website, Lauren McNamara said she believed the leaking of hundreds of thousands of classified documents was "irresponsible" but added: "I don't think Manning had any intention of assisting 'the enemy' in his actions."

The webchat came days after lawyers for Manning announced that McNamara would be called as a defence witness. Regarding the ethics of anticipating her own testimony in a public forum, McNamara said she was not doing anything wrong.

"None of this is private information or anything that hasn't been heard before," the 23-year-old said. "There's no secret weapon anyone is waiting to drop at the trial."

McNamara's involvement in the trial stems from online chats she had with Manning almost a year before his alleged leaking of state and army secrets to the whistle-blowing WikiLeaks website. Manning contacted McNamara – who at the time went by the name Zachary Antolak, but adopted the female persona "ZJ" online – in 2009, while preparing to be deployed in Iraq.

In a series of web chats which have since been made public, the young soldier confided about his sexuality and the bullying he had endured as a gay man in the army.

"It took them a while, but they started figuring me out, making fun of me, mocking me, harassing me, heating up with one or two physical attacks," Manning wrote.

It is thought that McNamara will be called by Manning's defence team, to testify that the solider had no intention of harming the US. Manning, 25, faces 22 charges related to the largest leak of state secrets in US history. The most serious of the counts he faces is of "aiding the enemy", which carries a maximum sentence of life in military custody without any chance of parole.

In her Reddit webchat, McNamara wrote: "If he did leak the documents he's accused of leaking (US diplomatic cables, the Iraq War Logs, the Afghan War Logs, and so on), then I imagine those charges would stand or fall on the facts of the matter... But the charge of aiding the enemy seems like it would be much more nebulous. I don't think Manning had any intention of assisting 'the enemy' in his actions.

"When I spoke with him, he seemed like someone who was concerned for the welfare and safety of US troops as well as foreign civilians in war zones."

But McNamara also suggested that Manning had been aware that his actions were illegal. She wrote: "I believe he was aware that what he was doing violated numerous laws and regulations – I mean, how could he not be?"

In response to another question, McNamara said that it was "irresponsible to release hundreds of thousands of documents, both diplomatic as well as from war zones, without taking the time to make sure they didn't contain sensitive or dangerous information".

McNamara defended herself against claims that talking about the case could undermine the defence. "This is probably the dumbest thing a witness in a high profile case can do," wrote one Reddit user. Another asked: "Is this legal?"

McNamara said: "I've never been advised against it, and I've been speaking elsewhere about this topic for some time."

In the US, a trial cannot be prejudiced by the prior publication of information that could risk influencing jury members. Nonetheless, many observers have questioned the wisdom of McNamara anticipating what she is due to testify, with some suggesting that her own words could be used by prosecutors to undermine her evidence.

Asked on Friday if Manning's lawyers had discussed what she would say in the trial, which is slated for June, McNamara replied: "Not really. We haven't reached that stage of things yet, and they've just laid out what their very general idea is: that my chats show someone who cared about his country, and that there's no way he was actually trying to aid the enemies of the US."