If she really wants to know there are programs such as WinSpy which are key loggers and can also be set to take snapshots of whatever is on the screen at time intervals that you can set, from every few seconds to minutes or hours.
When you install it theres a setting for the logon box to come up with a combination of keys that you select. Unless you hit those keys you never see the program running.
It doesnt show in the program files folder so no one but whoever installed it would know it was there and running.
Someone I know used it to check on her partners teenage son as she thought he may be going on sites she didnt want him visiting and talking to people she didnt want him talking to on messenger and such like.
Unfortunately it caught her partner out, they were planning a wedding a few months later, shed already spent a fortune on getting the dress made, and she saw that hed been logging onto various online dating sites and saying he was single and looking for a long term relationship
He denied doing it when she asked about it, then she showed him the evidence, needless to say the wedding was off and she kicked him out.