Is it permissible to attend gatherings or public places, such as a sewing institute, where some women wear immodest clothing, while trying to lower one's gaze? Is the place considered forbidden for me for this reason? And is it permissible to invite a friend to this occasion?

There is no harm in attending women’s gatherings and sitting among them, provided that one lowers the gaze from what is between a woman’s navel and knee, and that one denounces transgressions with wisdom and good admonition, and utilizes these gatherings to teach faith and goodness. There is no objection to inviting your friend to this occasion, and you bear no sin if she commits something unlawful according to the Sharia, because every soul earns on its own behalf. It is permissible to go to public places where wrongdoings may be present when there is a need, and one who is able to denounce them is sinful if they do not do so and no one else does it.