The 25-year-old shared the halfway lead on eight under with Scotland's Catriona Matthew but shot a six-over 78 to drop to two under.
Matthew struggled to a one-over 73 and is two off the pace.
American Danielle Kang, Japan's Haru Nomura and Korea's Jenny Shin share the lead on nine under.
England's Holly Clyburn saw her Australian Open challenge come to an end with a disastrous third round in Adelaide.