Kayla Mortellaro's 3-over 75 helped the cause for Arizona, which finished the day with a 1-under 143 for a two-round total of plus-4 292.
Selvaratnam, a 2006 runner-up at the U.S. Women's Mid-Amateur, had six birdies over the last nine holes at the Nicklaus Course, giving Arizona a two-shot lead on Alabama going into the final round on Thursday.
Kathy Hartwiger (72) and Courtney Trimble (73) helped Alabama, the 2005 runner-up, climb into second after the team had a 149 on Tuesday.
Florida, Tennessee and California are next at plus-10. Louisiana, which held a one-stroke lead after day one, struggled to a 154 on Wednesday and is a stroke further behind.
Defending champion Georgia has struggled with a mark of 29-over-par through two rounds.