Adjuncts to NAV2009

My GF and I share a computer ( actually it is her's)

 

It is a Vista Home with NAV2009 and use the windows Firewall.

 

All is well with it, except I try to tell her we need more than just teh NAV2009 to be safe, some adjunct on demand scanners

 

So she/we have realtime protection with NAV2009 and she has spybot as a secondary scanner. I think its not good enough, she says since Norton is primary, spybot is sufficient as an on demand secondary scanner. She has a friend who works It and he says that since Norton is our primary, spybot suffices as a secondary on demand scanner

My GF is funny in that she does NOT want to change things around. I know and you know that malewarebytes would be better. But again, she likes it as is.

 

so my question to everyone is, 

 

is Spybot sufficient  as a secondary scanner since NAV2009 is our primary security?