Could you provide some substantive evidence for that claim?
I don’t believe that to be true, it’d be very hard to conceal.
fyi...I work on embedded software, work with companies that develop circuit boards. You’d need to allocate some radio bandwidth that isn’t interfered with, have drivers in the OS running to drive the HW, with higher levels of software to interface with the OS....and do it all without somebody noticing? Not likely.
This incident sounds like they were able to infect her machine (maybe by remote hacking, maybe they had contact with her machine) with something that gave them the ability to instantiate a remote desktop session, take over the machine as an outside user as though being at the computer. This is done by IT departments every day to assist remote users.
The drivers do not have to be in the resident/legitimate OS. Nor does access to any data need to be obtained via the resident/legitimate OS. You are thinking far too conventionally.