coevolve, I understand your concern about security, but is native TRIM support really necessary with Mavericks? I think she will be happy to stick with OS X 10.9, which is where she was for the last 6 months or so.
Even if she decides to upgrade to Yosemite, she is such an infrequent software installer that I would not worry about her acquiring a hacked KEXT. Plus, she almost never strays from the App Store.
That said, if she does want Yosemite, I think there may be a compromise to the non-native TRIM problem. Could she simply activate Trim Enabler once a month briefly (for a few minutes? hours? 1 day?) to avoid performance degradation? That would avoid any potential problems such as having TRIM active all the time, one day updating OS X, and then being unable to reboot because the update enabled KEXT signing again.
Based on a performance review of the Crucial MX100 SSD (link below), it looks like activating TRIM "manually" brought performance back to "new" again. The only questionable part of that is exactly how they sent the TRIM command, and if it was a one-time deal or remained active throughout the "after TRIM" test. I could be wrong, but I'm imagining they did this: Manually activate TRIM, wait several minutes for TRIM to clean up the drive, repeat benchmark test.
http://www.xbitlabs.com/articles/storage/display/crucial-mx100_6.html