American officials said the whale appeared lethargic and lost almost 20 per cent of its body mass.
Scientists in Canada and the USA have been working together to save her life.
J50 was last seen Friday in Canadian waters, but researchers haven't spotted her pod since then.
"It's a great relief that she's still alive", said Paul Cottrell, marine mammals co-ordinator with the Department of Fisheries and Oceans. "We're hopeful that J-pod will come back into inland waters where we can continue our work for sample collection and veterinary assessment". "We're hoping she's going to make it".
Even with intervention, there is no guarantee that J50 will survive, but scientists still plan to try - if they can find her in time. If she takes the fish and keeps it down, biologists may also try to medicate fish before feeding her.
"Her body condition is on par with past situation we've seen where a calf did disappear", Lynn Barr of the National Oceanic and Atmosphere Association said during a conference call. The pod has been keeping to the outer coast and west end of the Strait of Juan de Fuca and environs.
"As you can tell we've had a lot of challenges in seeing them daily", Milstein said. "They could initially hear the whales through hydrophones and then they located them".
Cottrell couldn't say when the Canadian approvals would be in place, but said the process involves reviewing the proposal against the Species at Risk Act, consulting experts and considering regulations against feeding killer whales that were put in place to prevent habituation to humans.
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A picture taken by Brian Gisborne of Fisheries and Oceans Canada shows J50 swimming with her mother, J16.
Rowles said injections of antibiotics or sedatives have been given to other free-swimming whales or dolphins that were injured or entangled but it hasn't been done for free-swimming whales in this area.
Barre said operations testing for using live Chinook for nutritional support therapy and administering oral medication would be done with the Lummi tribe and the Whale Sanctuary Project - without whales present. Researchers cite a shortage of chinook salmon as one of the main reasons for the orcas' decline.
She said it became evident that "we needed to intervene to determine potentially what was the cause and whether there was anything we could do to assist her".
It's not unusual for wild whales to be out of sight for some time, but J-50's condition was so poor it's not clear how long she has left.
"Hopefully, they are doing well and foraging and doing what they need to do".
The young orca was glimpsed again Wednesday swimming with her mother off the tip of the Olympic Peninsula, in USA waters.