Two-year-old Casey girl Addison Worsnop-Cottle was selected by Ronald McDonald House to do the honours at a ceremony outside the National Library, starting at 7.30pm.

The little girl, who loves The Wiggles and Christmas movies, has been braver than brave, fighting short bowel syndrome since she was born.

Addison - Addie - spent the first 10 months of her life in the Canberra Hospital. At the time, her mum Natalie Worsnop was living in Tumut and dad Damien Cottle was working in Sydney. So Ronald McDonald House in Canberra became their home away from home so they could be close to their little girl.

Addie has shown remarkable resilience - she still needs to be connected to a home IV 18 hours a day to ensure her body gets the nutrients it needs.

When Ronald McDonald House rang to let the family know Addie had been selected to switch on the illuminations at Enlighten, mum Natalie was a little overwhelmed.

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"It was lovely but a bit daunting as I'm quite shy," she said.

Dad Damien, a gregarious Irishman, has no such problem. "I'm the opposite," he said, with a laugh.

Enlighten will provide some joy for the family, with Addie's parents proud that she has endured so much but is still a happy girl.

"She is very good. There are days when she's really bored but she's still good," Natalie said.