There are a number of ways to set policies in Vista. Try this one:
o Click on Windows Vista Start, and in the search area type in “secpol.msc” and click Enter. (You may receive a prompt from UAC,(User Account Control) approve/login and proceed).
o In the left list, choose “Local Policies“ and then “Security Options“.
o Set “Accounts: Administrator account status” to Enabled.
o Set “User Account Control: Admin Approval Mode for the Built-in Administrator account” to Disabled.
o Set "User Account Control: Detect application installations and prompt for elevation" to Enabled.
Have your niece set up and administrator account with a password (control panel, Users). That should do it.
(You can also go to Start/Run and type in gpedit.msc and do it from there.)
WinPatrol will run on Vista, I have it installed on W7 64 bit. Spyware Guard will not but Super AntiSpyware will also run on Vista.