The sister of murdered Brisbane mother Allison Baden-Clay has vowed her killer will be brought to justice.

Vanessa Fowler told mourners on Friday many questions remain unanswered about her sister's death.

"There are many pieces of a puzzle that need to be put together and we, your family, pledge to you that we will have the questions answered," she said through tears at the funeral service at Ipswich, west of Brisbane.

"We will bring you justice because you deserve nothing less."

Mrs Fowler delivered an emotional eulogy.

"Allison's life was filled with music, dance, love and laughter," she said.

"Ashley (Dickie, Mrs Baden Clay's brother) and I would never have imagined we would be standing here today reading this eulogy.

"Our Allison has left this earth under such horrific circumstances at such a young age .. she has done so much, yet had

so much to live for, and oh so much to do."

Mrs Fowler described her sister as "a high achiever, a model mum and an unselfish soul" who devoted herself to her children.

Mrs Baden-Clay had managed to achieve great things under sometimes difficult circumstances and was able to rise above

adversity, her sister said.

Mrs Baden-Clay's husband Gerard Baden-Clay, who reported her missing on April 20, was among the mourners at St Paul's Cathedral, along with the couple's three young daughters.

More than 600 mourners packed St Paul's Anglican Church in Ipswich to farewell the 43-year-old mother of three, whose body was found in a creek bed 11 days ago.

Mrs Baden-Clay, 43, went missing on April 19, after leaving home for a late night walk.

Her husband reported her missing early the next day, and her body was found on a creek bank at Anstead on May 1, about 10 kilometres from the family home at Brookfield.