Before sticking your foot in your mouth, you should qualify your answer to her:

The usual residential system that has been setup for motion recording, 8-10fps, 4-8 cams, and a 1TB HD; would typically get about 1-3 months of recording (depending on a great many factors).

If her 'other' system is getting 2 years of recordings, then a few things are happening. The video is being recorded at a very low frame rate (1fps or less), high compression, CIF resolution, large TB hard drive(s), and almost no activity.

If she states that the recordings are HD looking, fluid motion, and a lot of activity - then I would say she's full of crap. It is one of those mental issues that people want something to be true that is not.