How to protect a PC against sensitive data access by malicious app/driver
A driver, by definition, is part of the operating system. As such, whenever someone is able to place a malicious driver, it gets access at a system level of privileges. That means it can access every single bit of memory your computer has.
You lost the game.
The only way to effectively counter this are air-gap security. Ie. place your machine in a room without any link to the outside (and that would include unintentional RF radiation, eg by rhythmically bursting a PCIe bus, or by actually RF transmitting malicious hardware), and monitor personally who accesses the computer.
I'd love to say something uplifting about not having the driver installed in the hypervising operating system, but in a lesser privileged VM – but the reality is that you probably want to use the device in the same context that you're developing in (otherwise, you'd simply not install the device in a sensitive environment, at all), so that basically simply doesn't help.
Note that the problem doesn't stop at the software level – if your hardware is a PCIe, CardBus, PCI, AGP, PCMCIA, ISA, PXI, PCI-X, FireWire, Thunderbolt, or one of many storage device classes (Floppy, IDE, probably a lot of Sata devices, M.2,), typical "tightly coupled" buses like HyperTransport, AHB then it might get DMA – and thus, exactly that, Direct Memory Access, without any chance of the Operating system, an antivirus software or even just the CPU to interfere. Usages of this mechanism to read out, and exfiltrate, the contents of a PC's complete RAM have been demonstrated numerous times.
You use the USB tag, but you don't explain it in your question – USB itself doesn't give the devices DMA capabilities, but many USB host chipsets and device drivers actually have bugs that allow USB devices to essentially get memory access. Note that this leaves the "malicious driver" domain, and enters the "buggy host-integrated hardware" and "buggy driver" domain – and everyone having ever read a piece of consumer windows driver will agree that this class of drivers is the dominant one.
All in all, installing malicious hardware in your machines is pretty much the "evil maid" scenario, only that you are the evil maid yourself.