Is this the snorkelling set your daughter is considering purchasing?
If so, I'm afraid, as a man,
I can't offer direct personal experience of the fins pictured.
Nevertheless, I've snorkelled (never scuba-dived) for half a century in the Mediterranean, English North Sea and the USA, so I've learnt a few things over the years. One of my most memorable snorkelling trips was to La Jolla Cove in Southern California, where I observed snorkellers of all ages enjoying themselves. They all wore different kinds of fins. Some were in adjustable open-heel scuba-style fins. Others were in bodyboarding-style fixed-heel all-rubber fins. Still others were swimming with long-bladed full-foot freediving-style fins. Yet others, like myself, wore all-rubber swim training-style full-foot fins with short or standard blades. I think I spotted somebody else in a pair of Force Fins. The common factor was that we were all having a great time, none of us felt hampered by the inadequacy of our chosen fins. Almost any kind of fin can be used in snorkelling.
A couple of criteria which do matter in fin selection, whether for scuba, snorkelling or freediving, are fit and purpose. Foot pockets have to match foot dimensions not only in terms of foot length - I see the Diva fins come in two sizes - but also with respect to foot width and arch height. This is why it's important to try any fins on for size. Too loose and the fins will raise blisters or fall off. Too tight and your daughter is likely to experience foot cramps. You might also want to consider whether she will be wearing socks or booties with the fins for warmth and protection. If so, you need to check whether the fins still fit when wearing socks or booties. The second criterion, purpose, relates to what kind of snorkelling your daughter is contemplating. Fins aren't worn for speed, but for power, endurance and manoeuvrability in the water. No single fin combines these attributes in equal measure. She might want to practise with her new fins before she embarks on her Caribbean cruise so that they become a natural extension of her feet.
So, to sum up: would I snorkel with these Diva fins? Well, no I wouldn't, not only because they're pink, but also because I prefer traditional, all-rubber full-foot fins, the kind that were the norm back when I started in the early 1960s. This said, everybody's different and finding the perfect fin for your daughter is a something of a personal odyssey and nobody can do it for you. So forget about brand names for the moment and concentrate first on finding a pair that fit. If your daughter is fortunate enough to find several matching her foot dimensions, then consider next whether she prefers open-heel or full-foot fins. Contrary to popular belief, socks and booties can be worn with full-foot fins as well as open-heel fins, but you have to check for fit. Then, and only then, consider other matters such as the stiffness and length of the blade, which will determine whether your daughter experiences fatigue during prolonged use.
My best wishes to your daughter when she snorkels in the Caribbean. Snorkelling is such a wonderful, inexpensive, spontaneous pastime. I've had a great time this summer snorkelling in the early mornings in the North Sea off the coast of North East England. I wear a suit to keep warm, I wear an oval mask on my head and a pair of traditional all-rubber full-foot fins on my feet and I'm happy with every item of my snorkelling gear. What suits me, of course, won't suit everybody, so I'm not recommending that you follow my lead!