There's nothing inherently wrong with speaking rapidly. The truth is, is that the speaker is understood more often than they are not when enunciation is not an issue. Take, for instance, reading... If you were to occlude the bottom half of every letter in English, one would generally still be able to read. I remember reading somewhere that that's how the eyes scan text in interpreting it.
I can speak rapidly (and do). I can also, ofc, speak in a very punctuated manner. So why do I not do one or the other consistently? Delivery.
Timing is everything. (Read fast)
Timing... is... everything. (Read with emphasis and pausing)
Less dramatically, but more colloquially, one could play with various timings and emphasis on, "Oh"
In drama class in High School, we had to do an entire skit with 2 words: Why and Because
It was very informative on how the pace of speaking and the emphasis on syllables could imply so very much.
With some background conversation and exercises based on the above, one could then draw the following conclusion: Just like we deplore sitting through 60 seconds of a monotone speaker, one who speaks in a very rapid manner continuously is a similar bore.
Instead of trying to follow any kind of strict breathing/speaking regimen, perhaps encouraging playing with her speech patterns to make them more interesting and powerful to those listening would be of interest and benefit to her?