Bringing my Mexican girlfriend to Vancouver

I'm a Canadian citizen who wants to bring my Mexican girlfriend to Vancouver to meet my family and experience Canadian lifestyle before we return to Mexico to marry and begin the immigration process there next year (apparently it's faster outside of Canada). Since she's never been overseas on her own, I would like to fly with her and go through immigration together to try to ensure her entry, even though as a Mexican citizen she is not required to obtain a Temporary Resident Visa.

The problem is, I've heard that just by being there with her they might deny her entry thinking that she'll stay and work. Will my presence help or hinder? Someone suggested she should go through herself and say she'll be staying with a girlfriend... but the last thing we want to do is have to lie. Would a letter of invitation from me be any use? We will make sure she has lots of cash, a bank statement, proof of registration as a teacher for the fall semester in Mexico. I'm hoping that this will be enough to assure the Immigration official that she will indeed only be staying two months...

I read a horror story about a Mexican girl coming to visit her Canadian Boyfriend for a legitimate holiday, holding sufficient cash and even proof of her good job back in Mexico -- she was refused entry and sent back back the next day after spending the night in a cell. This is the last thing I want to have happen to my girlfriend and her parents would kill me!