Amy Colle Dieng was arrested on Thursday for "offending the head of state and broadcasting fake news," a police source told AFP after audio of her lashing out at the president created a social media storm in recent days.
In the recording shared via the WhatsApp messaging service and then uploaded to YouTube, she calls Sall a "sai sai", or "scoundrel" in the local Wolof language, who "operates in the shadows" to achieve his aims.
Dieng is also heard declaring her support for ex- president Abdoulaye Wade, who stood as an opposition candidate in last Sunday's legislative elections, and she criticises administrative errors that marred the vote.
State prosecutor Serigne Bassirou Gueye said the authorities had observed an uptick in "reprehensible" behaviour including the sharing of "obscene, offensive" images and memes, adding that cybercrime laws allowed for sentences of up to a decade for such offences.
More From This Section
A second woman was arrested on Friday for broadcasting ethnic slurs in a video shared online, a security source told AFP, speaking just hours after the prosecutor's comments.
Dieng's case comes after four people were charged in June with "offending public morals" for distributing a fake image of Sall naked, also via WhatsApp.
Results from Sunday's election are due on Friday, with a landslide victory for Sall's ruling coalition expected.
Senegal is known for its largely peaceful democratic traditions and freedom of the press, though rights advocates hit out at the government over the WhatsApp image case.