The Aboyne teenager came home in 33 as she carded a three-under-par 69 in the second round on the Montgomerie Course at Carton House.
Coupled with a 72 from Connie Jaffrey, that lifted the Scots up a spot to joint-12th on one-over as the US stormed into the lead on 16-under on the back of 65s from Jennifer Kupcho and Kirtsen Gillman.
“The past couple of days have been good fun, on and off the golf course,” said McWilliam. “I have played well both days, holing a lot of long putts today which helps. The plan for the next couple of days is to enjoy it and finish in the top 10 as a team.
“The level of competition this year is very high, with the US team consisting of the top three players in the world.
“The field also includes a 70-year-old (Beatriz Arenas of Guatemala), which is amazing. It just proves you can play golf at any age at a top level.”
Kupcho and Gillman were both bogey-free on the O’Meara Course as the US moved into a one-shot lead over defending champions Korea, with first-round pacesetters Japan two shots futher back in third.
On the European Tour, it was an encouraging start in the Made in Denmark event for three Scots battling to hang on to their cards for next season.
David Drysdale, who sits 127th in the Race to Dubai, opened with a four-under 68 at Silkeborg Golf Club while Richie Ramsay (132nd) and Marc Warren (141st) shot 69 and 70 respectively.
Englishman Jonathan “Jigger” Thomson, who is even further down the Order of Merit after a poor rookie season, carded nine birdies to set the pace with an eight-under-par 64.
On the Challenge Tour, David Law opened with a four-under 66 to sit joint-seventh after the first round of the Cordon Golf Open on the Challenge Tour.
As Portugal’s Jose-Filipe set the pace in Pleneuf, Jack McDonald (67), Ross Kellett (68) and Sam Locke (69) also opened with sub-par efforts.
On the PGA EuroPro Tour, Paul McKechnie is in contention heading into the final round of
The Prem Group Irish Masters at Tulfarris Hotel and Golf Resort.
A former No 1 on the third-tier circuit, the Braids Hills Golf Centre player shot a second-round 66 for seven-under to sit joint-second, three behind home player John-Ross Galbraith (68-66).
McKechnie was bogey-free, making birdies at the third, seventh and eighth going out before adding three on the spin from the 13th.
John Henry is tied for 10th on five-under while Conor O’Neil, Craig Lawrie and Ryan Campbell are all sitting in a share of 15th spot.