Arrgh,
Here's why that didn't work, and why you're essentially the victim of sh1tty community advice.
Her: I have a boyfriend, it kinda matters
You: No it doesn't, you're stupid
Now, don't get me wrong, the reason why the goldfish line and that other one have been written about is that it has worked in the past, and may work in some specific situations.
The reason why it usually won't can be traced all the way back to "How to Win Friends and Influence People". There, Dale Carnegie essentially said that when two people argue, no one wins. When she presented her point, you essentially argued with her and told her she was wrong.
Let's compare this to some good community advice that highlights this point concerning LMR. When a girl starts to hesitate in the sack, the equivalent to what you did would be to say something like, "why hesitate, we should fark". You're arguing with her and trying to convince her why she should sleep with you.
Anyone who's read the game will tell you that this isn't the way to sleep with her. Instead, you agree with her... "Of course, you're right, we should slow down, what are you trying to do to me?", and let your subtle actions say something different, or you shut her off.
Applying that advice to your situation, instead of arguing with her which will usually just push her away for good, agree. "Oh, that's great, how long have you guys been together, how's that going", and then do the sh1t I said and sneak in the back door - literally and figuratively.
Don't just believe some sh1t you read on the internet from some internet marketer masquerading as a "guru" unless it actually makes sense and works for you.