Moderator, Air Canada; FlyerTalk Evangelist
Join Date: Feb 2015
Location: YYC
Programs: AC SE MM, FB Plat, WS Plat, BA Silver, DL GM, Marriott Plat, Hilton Gold, Accor Silver
Posts: 16,771
If your friend has the option of buying a lounge pass with her ticket on the flight, either when booking or later through the AC website's Manage My Bookings area, and she buys the pass, she'll be able to get in. Note though that the access needs to be purchased in advance, not at the airport.
Whether you're with her doesn't matter since you're not entitled to bring a guest and she'll have access if she buys a pass, regardless of whether you're there.