The world number one, who already has three titles to her name this season and is going for her third tournament win in as many weeks, carded a second consecutive four-under 68 to sit eight under overall heading into the weekend.
That put the Taiwanese player a shot ahead of South Korea's Haeji Kang and two clear of Kang's compatriot Yoo Sun-young and Lindsey Wright of Australia.
Yoo carded a second straight 69 and thrilled the crowd with an eagle at the par-five second.
Overnight leader Amy Yang hit a two-over 74 to sit joint eighth on four under overall.
Despite a one-over second round, England's Jodi Ewart was leading the British challenge on two under in a share of 16th.