He had a feeling that she was very light [like e.g. a feather], as if even the light puffs of breeze blowing this morning might send her sailing away like a dandelion gone to seed. - Have you ever blown on a dandelion flower when it has lots of seeds? - @Michael_Harvey

To add on, I think this "exaggeration" might be Ray's love towards her mother.

He had a feeling that she was very light [like e.g. a feather], as if even the light puffs of breeze blowing this morning might send her sailing away like a dandelion gone to seed. - Have you ever blown on a dandelion flower when it has lots of seeds? - @Michael_Harvey

To add on, I think this "exaggeration" might be Ray's love towards his mother.