Cavaliers can have a long soft palate & other anatomical features that slightly compromise their breathing. Often the only consequence is a variety of interesting noises that accompany whatever activity they are engaged in.
Brian, I know how you love your girls, so I am reluctant to worry you, but I do think if Daisy is getting distressed, and there are things that make you feel uneasy, then you may be wise to consult your vet.
Heart problems in this breed can suddenly show up & worsen quickly and better a wasted journey than a poorly dog.
Cavaliers......Tommy Tuppence 2000-2012 and a half share of Faith.
Japanese Chins.... Dandy, Benny, Bridgette and Hana.