An ustadha who lives in Canada, in her fatwa says that it is permissible for women to attend a mixed gym if there is no music, if they are dressed mod

Answer

The 'ustaadha' you mention is actual a shaitaanah (a she-devil). She is among the Habaailush Shaitaan (Traps of Iblees) which Allah Ta'ala had granted shaitaan in response to his supplication on the occasion when he was ignominiously kicked out of the heavens to lead an accursed life of deception and villainy on earth. Shaitaan enlists these types of moron, lewd women to ply his trade of deception. Every Muslim whose thinking ability has not been cast into disequilibrium by westernism will understand that the copro-fatwa of the shaitaanah is the effect of mental dissonance. The Imaani conscience of a Mu'min suffices to rebuff the rubbish fatwa of the shaitaanah.