Yes, VM's can work, and have advantages
But if her long-term aim is to use only Linux, she should run LInux on the bare machine. The virtualisation hardware on modern processors has cut down drastically on the virtualisation overhead, making it practical, and it may well turn out to be her preferred mode of operation on her final laptop
I can't run a virtual machine with any speed on my ancient laptop; it just doesn't have the right hardware. Her old laptop may be as decrepit s mine; she needs to be aware that dual boot is an alternative.
And even so, aren't there still issues with high-speed graphics? I've heard rumours that they've started making some graphics processors so they can be partitioned for virtual machines, but I hadn't heard that they were actually practical yet.