You'll get people who are opposed to parks like SW + DC. It is very rare that they actually visit such a park to see for themself or even take the time to consider what good is being done in the wider scheme of things.
SW and DC work very hard to put their animals in the best situations possible, they also do major work in rescueing and caring for sick and injured animals hopefully to release in the wild. Not all can be, I believe all the manatees at SW are rescued and their injuries, while no longer painful or life threatening, are too extensive to allow them to live comfortably in the wild. The most important work SW and DC do is in raising awareness of the risks these animals face in the wild. IMHO good parks like SW do far more to make people aware of the beauty of these animals and what is needed to be done than any amount of work done by these so called "animal rights" activists.
Humans will only save what they care about, and they will only care about what they have the chance to see. Parks like SW offer many people the chance to see what's out there and what can and should be saved. For many kids that don't live near the oceans it's the only chance they have to see a dolphin. If they've never seen one it's unlikely they'll be too worried about how their actions, in say Boise Idaho, impact on the marine creatures of the world.
I would agree the best place for dolphins is in the oceans, but unless something is done to protect their environment there will be no where those dolphins can safely live. If a small number of creatures have a safe, comfortable but perhaps less than perfect existance in order to make a difference then, IMHO it's a price worth paying. Your friend displays a touching naievity, in the real world SW and DC can and do make a difference. I don't believe her and her kind have as much effect.
Please, when you've been to the park do come back and tell us if you think the dolphins are cruelly treated. If you witness the care and attention their trainers pay them I think you'll be pleasantly suprised.