We tend to think of 'flash in the pan' celebrities as being a comparatively recent invention - the product of 'one hit wonder' musicians, or reality television stars. That isn't quite the case. It would be a little unfair to call Charo a flash in the pan, but her career both started and ended in the 1970s.
It's hard to say why her fame didn't last longer. At one point, she was everywhere. Any time you switched on the television and saw a variety show, you'd see Charo singing. She sold out shows in Las Vegas, headlining bills which contained people who could go on to have much more enduring fame. Charo may not have been a big deal after the 70s were over, but people definitely enjoyed her and her (largely staged) pigeon English style of delivery at the time.