Yeah, it's a tough field to get in to. I was a husbandry biologist at a couple aquariums (mostly sharks, rays and turtles), but also helped out the mammal teams as needed (tigers and otters in particular).
Getting to care for cold blooded animals was hard enough; the competition to care for and train cute warm blooded creatures is absolutely savage.
If there's no Marine Biology program then a major/minor or double-major combo of psychology/biology is pretty common.
Getting husbandry experience of any kind, any way possible, is absolutely key. This means anything from working at Pet Smart to volunteering at a shelter, volunteering and/or internships at local Zoos or Aquariums to doing university research involving animals, etc...
Obviously, being a strong swimmer is important. Scuba diving experience will likely be required as well.
Jobs are few and far between, and it's absolutely an industry where who you know counts. So I would advise she expand her aspirations beyond just working with dolphins. I know a few people who started with dolphins and ended up working with elephants or tigers or primates, etc...
Places like Disney and Seaworld (and probably lots of others) have super strict appearance codes as well, which restrict everything from no visible tattoos to acceptable hair styles and dye colors.