EJ has weathered a snow storm and harassment from rival ospreys while incubating her clutch of three eggs. All hatched over the past few days.
The RSPB suspects mate Odin, who was bringing fish to the chicks, was frightened off by another male.
On Monday, an osprey was at the nest with a fish but the chicks were dead.
The bird is thought to have been EJ.
RSPB Scotland said she was expected to remain at the nest and guard it against being taken over by other females.
It is possible to view the nest site via a webcam. Footage on Monday morning appeared to show the nest had been abandoned.
Later, on occasions, an adult osprey was seen at the nest, at one point with a fish.
At the weekend, RSPB Scotland said it had decided not to intervene in what it described "heart breaking" but natural process playing out at its reserve.
EJ, who is 20 years old this year, has been visiting Loch Garten for 15 years and has reared 25 chicks over that time with mate Odin and other males.
The nest is in a tree on an RSPB Scotland reserve.
EJ and her long-term mate Odin are the most successful breeding pair at the Loch Garten site.
Over previous seasons, 17 of their chicks have fledged.
Ospreys migrate from west Africa to Scotland to breed and can be seen hunting for fish from rivers and lochs.
EJ's breeding seasons have been fraught with drama in the past.
Incidents have included eggs being kicked out of the nest by a male bird and battles between EJs and rival females over the nest.
All three chicks being raised by a well-known female osprey in the Cairngorms have died, RSPB Scotland has confirmed.