Lolita was kept in cramped environs, and her former tankmate Hugo died after smashing his head into the tank walls in what is believed to be a suicide, Ms Daals said.
"It's ludicrous to have such a huge, beautiful creature that travels hundreds of miles a day stuck in basically a bathtub...they're still not doing anything about it."
Despite several protests and court battles, Lolita remained at the Seaquarium with no release in sight, Ms Daals, 29, said.
In January, hundreds of people marched to the oceanarium to call for the orca's release.
In July, groups seeking Lolita's release reportedly sued the Seaquarium and its parent company Palace Entertainment, claiming the orca's living conditions breached the US Endangered Species Act.
"A demonstration like [this] has never been done before so I'm hoping that we gain as much global attention as possible and therefore put more pressure on Palace Entertainment," Ms Daals said.
Some protesters calling for Lolita's release had previously made placards asking 'could you live in a bathtub?' or drawing the orca in a bathtub, as an analogy for Lolita's tank, she said.
"So, I thought I'd put myself in one."
Ms Daals was planning to stage her demonstration in January.
She was considering doing tricks whenever she wanted food, to "simulate" the orca's situation.
Ms Daals would only leave the tub to go to the toilet.
Several animal rights groups, including People for the Ethical Treatment of Animals (PETA), were helping her organise the protest, she said.
A GoFundMe website page was also being considered.
The bathtub would be situated as close as possible to the Seaquarium, but not on its property, she said.
The Seaquarium has previously rejected claims Lolita is cruelly treated.
The oceanarium said Lolita was well cared for and had been in captivity so long that releasing her would be "cruel and traumatic", the Guardian reported in July.
Lolita was captured in Puget Sound near Seattle, some 5300km from Miami, in 1970.
"I don't think you'd put any family member in a bathtub and keep them there if you really cared about them," Ms Daals said.
"Even if she only survives a year or two in the ocean, at least she'll get a second chance at freedom."
She hoped the oceanarium reconsidered its position.
"I think she's earned them so many millions of dollars now, that she's earned her retirement."
Orca Factbox:
• Orcas hunt in pods or family groups of up to 40 individuals.
• They learn local and complex languages retained for many generations, and have exceptional bio-sonar, or echolocation abilities.
• Orcas live on average 50 to 80 years in the wild.
• Orcas give birth every three to ten years, after a 17-month pregnancy.
• Scientific name: Orcinus orca. Common names are orca, killer whale, blackfish, grampus and killer.
• Males attain an average length of 6-8m and weight of 3600-5400 kg.
• Females grow on average to 5-7 m and weigh between 1300-2700 kg.
(Sources: National Geographic, phys.org, Center for Whale Research)
