You could certainly do that. However, just make sure you keep them in a secure place and don't have too many lying around with pics on them. You never know if the SO might come across one and insert it into a camera or SD Card reader. The likelihood I suppose depends on how technologically adept she is. But the more incriminating cards you have lying around, the higher the chance you might get busted.
Like I said, since they're so cheap now(I think 8GB is HKD100 or less now) there's no need to skimp on capacity. If you have just one card you use for punting pictures it will be easier to keep track of.
Other option is to use the 32MB cards as you intended and immediately upload to a desktop and use the True Crypt as JD suggests above
Cheers and look forward to reading your reports!
