

Are they looking at the files on her MacBook or something?
If the apps are logged in yes, that’s what they do. The agents have a lot of discretion so it’s sort of up to them how much they want to search around on a phone/laptop/whatever but I assume they would look at every single social media app for starters. Essentially any app currently logged into an electronic device would be fair game for an agent to review. And since CPB can ask for your phone/whatever password (or ask you to unlock it for them) that will give them access to basically any logged in app on the device.
I don’t know if OP is referring to a U.S. citizen or something else so the specific rules that apply may be different but that’s the general idea.
It’s been a thing, not specifically just Canada
https://www.wired.com/story/phone-searches-at-the-us-border-hit-a-record-high/
That said I don’t personally know any canadian citizens that have traveled in/out of the U.S recently. Not too sure if it relates to OP’s question, OP never mentioned canadian citizens only that they has a GF that goes to school in Canada.