A Western Australian mother jailed over a fatal crash that killed her twin daughters is set to be released from prison.

A court heard this week that seven-year-olds Macey and Riley were wearing seatbelts but not in car seats when Van Oyen closed her eyes for a split second before crashing.

The girls were flung from the car when it slammed into a tree and flipped near Merredin, about 230 kilometres east of Perth, last February.

There had been gasps in the courtroom when Van Oyen was sentenced to serve two months in prison and six in the community over two counts of careless driving causing death.

She will be released after just two nights in prison after a judge agreed to hear the appeal.

“I am happy that she will be out with us today,” stepmother Heather Van Oyen said.

“I don’t think any one of us will ever know the depth of the impact that Rachel suffers every day and this lifelong sentence she has.”

Despite granting Van Oyen bail, the judge told her she didn’t want to provide false hope that she would not be returning to prison at a later date, saying the bail decision did not indicate what the outcome of the appeal might be.

During sentencing, the court was told Van Oyen was neither fatigued nor speeding but closed her eyes for a split second, veering left, then overcorrecting.