it's possible, but you'll have to create a wrapper around
Mail - ie a program that takes care of starting
Mail.
Anyway, if somebody has access to your wife's account on the computer, they can just access the email stored on the computer itself directly in the file system - it's stored in plain text files one email at a time.
It's not that easy to implement, and the solution will depend on your wife's particular situation:
- is she the only one using the computer
- how secure a solution do you want
- what kind of email account does she use
- etc
I don't actually think the your wife's problem is that anyone can start
Mail, but rather the access to the actual email itself. If the latter is the case, then the best solution will be to encrypt her local mail storage.
PGP and
Disk Utility can both provide solutions for that.
Anyway, I'm not aware of any off-the-shelf solution for your problem a originally stated, but I'ld be willing to give it a try if you should want so - could be a fun project
