The Duchess of Sussex has encouraged people to use their voice “to advocate for what is right” during a discussion on the importance of representation in media and entertainment.

Meghan led a keynote speech on Friday titled Breaking Barriers, Shaping Narratives: How Women Lead On And Off The Screen which marked International Women’s Day, alongside speakers including US actress Brooke Shields.

“Your voice is not small, it just needs to be heard,” former Suits actress Meghan said, during the annual SXSW Conference.

Meghan said that when she was 11 years old she wrote to Procter & Gamble and got an advert changed from saying dish washing liquid was for women, but for people all over America.

The 42-year-old said: “It’s funny to look back at it now as it was before social media where you had a reach that was so much greater, it was just an 11-year-old with a pen and paper but goes to show if you know there is something wrong and you’re using your voice to advocate for what is right, that really land and resonate with people.”

Shields joked: “This is one of the ways we’re different, when I was 11 I was playing a prostitute,” recalling her starring role in 1978 film Pretty Baby.

During the session, Meghan emphasised that “representation matters”.

“The key thing that I think needs to be focused on in terms of equity is it’s not a zero-sum game, just because someone else has the same advantage that you do doesn’t mean that you’re losing anything, and actually create an environment that is so inclusive where people feel as if they have a seat at the table – as they should,” she said.

In an earlier session, Modern Family star Julie Bowen revealed that the Duke of Sussex was also present at the event in Austin, Texas.

Meghan’s appearance comes as the Princess of Wales recovers from abdominal surgery in the UK, and Kate’s maternal uncle Gary Goldsmith appears on Celebrity Big Brother.

During his five days on the ITV reality show, Goldsmith told his housemates that Meghan put a “stick in the spokes” when she was first introduced to the royal family, creating “so much drama that I don’t generally think is there”.

The keynote speech was presented by Meghan and Harry’s The Archewell Foundation and The 19th, the national nonprofit newsroom reporting on gender, politics and policy.