When can't an adjective clause be redued to an adjective phrase

Please tell me in what cases an adjective clause cannot be reduced to an adjective phrase. Please see below:
The snow which fell overnight has turned into ice.
The girl who fell on the ice broke her arm.
From the above sentences, some English teachers argued that they can’t be reduced to
The snow falling overnight has turned into ice.
The girl falling on the ice broke her arm.
They commented that they preferred the full version of adjective clauses to the reductions.
Can you please find out the correct answers ? Wis

In my opinion, both of them are correct. But in an exam, you should write a full sentence.