LOL Tik, I have a gym buddy just like that. And the she'll always say to me something like *what weight was I lifting...I thought I was benching 5's*

I usually end up telling her it was 15 or so, which she does with no problem.
But she's gotten so much better, they just need a push, and yes sometimes you have to just say "hey...I bet you're a lot stronger, you should try X weight for a few reps and see if it works for you".