Rey is described in the official novelisation as being a 'conduit' for the power of the (former) Jedi Order rather than possessing their power to herself. After the fight is over, there's no good evidence that she still has this vast Force power, merely returning to that of a single Jedi.
Presences filled her awareness, some recent, some ancient, some still
anchored to the living in a strange way. Rey didn’t understand. But
Alone, never have you been.
Every Jedi who ever lived, lives in you.
The Force surrounds you.
Let it guide you.
As it guided us.
Palpatine had wanted Rey for himself. But she chose to be their
conduit. Their vessel. She was a Jedi.
Rey moved an arm. Then a shoulder. She let the voices surround her,
fill her, strengthen her. She turned over, placed a palm to the
ground, pushed up.
We stand behind you.
Rise in the Force.
Later on when we see her, she's back to being ordinary old Jedi Rey. She can still commune with Force ghosts, but she's not filled with their voices and powers.
So many memories here. She could feel them—yearning, loss, worry,
desperation, love—and not just Luke’s. Two generations of Skywalkers
had visited this place.
A cavelike entrance in the wall drew her forward. As she passed into
shadow and her eyes adjusted, she noted a long dining table, covered
with dust. She ran a finger through the dust, tracing a line of soft
blue. Luke had dined here. And also—she reached out, sensing—Anakin?