well I for one am happy with your thread since singing is discussed and there are not so many threads about it.
I think you are right in telling her to first learn the melody with rhythm the way it is. It is difficult when you don't read notes. I write the melodies in sibelius to learn exactly. I'm not at my best singing the exact written rhythm right away, but I have a natural feel where the measures are, so I use my own timing but stay within the measure pulse. My coach has another term for the floating but I can't recall now how she calls it. When I'll remember I'll get back to you on that.
I think you could advise her to clap the measures while practising so she can hear how and where they are. What also helps is to move/dance with a specific body part on the 126.96.36.199, maybe shake hips or tap a foot so that way you can feel the measure in your body.
I also use band in a box to practise with and that way you can practise the floating too. If she doesn't hear that she goes wrong, I'm not sure if this will help and think you have giving the best advice you could give.