Does stuttering go in phases? Moments of hardly any stutter than a period time of severe stutter and than back?

Does stuttering go in phases? Moments of hardly any stutter than a period time of severe stutter and than back? My wife told me she has been stuttering since she was 5 years old. She also told me that her stutter was at it's most severe during high school (she grew up in Puerto Rico where there wasn't a proper speech therapy at the time (and also regardless of being a stutterer or not - high school is a stressful/anxious time for anyone)). Eventually my wife's stutter calmed down when got older and began to speak English (her stutter is much more noticeable than in her native Spanish. She's also learning some Polish (I am from Poland)). However, recently my wife's stutter has become more noticeable (her hands shake and head shake when she's blocked - these moments has experienced when she was younger). Is it possible for those who stutter to have up-swings and the down-swings. My wife said it's possible because stuttering is very unpredictable.