For the purposes of the average person the tech guy in your op is absolutely 100% correct.
All the platforms listed use transport encryption and that’s enough to avoid mitm surveillance which is enough for most people.
Most people’s “threat model” is the police or a pi. All the apps listed including signal have to comply with orders from American police and have “sidechain attacks” that involve stuff like getting some member of the groupchat’s device and scrolling up or tricking someone into giving up sensitive information.
Does she want this?
If so then just set her up exactly what you have so you can easily help when there’s a problem.
If not then get her the computer she actually wants.