No offence to your Aunt but I thoroughly disagree with this. Sometimes it's true, actually. But the reality of any art is that there is often as much perspiration as inspiration and I don't believe listeners have some unique insight that enables them to instantly 'spot' a forced line or lyric. Lots of lyrics that I think are great were identified as throwaways by their writers. Similarly, lyrics or lines that I thought were shitty are held in great inspirational esteem by their writers. It works both ways.
Sometimes, a lyric just comes so easilly. Other times it's like pulling teeth. But the craft of songwriting involves sometimes having to force bits. That's how people can write songs for musicals and soundtracks and movies.
It's equally true that, as you point out, sometimes, it's just not coming and you gotta walk away and return to it hours, days, months, even years later.