How should one deal with a mother who works in the abaya industry, which is suspected of being Islamically unlawful, without disobeying her, knowing that she spends from this money?

The manufacturing and tailoring of clothes, such as abayas and other garments, is permissible unless they are used for something forbidden, like clothes that reveal a woman's adornment in front of non-mahram men. Allah Almighty said: (And cooperate in righteousness and piety, but do not cooperate in sin and aggression). If it is highly probable that the buyer will use them for something forbidden, then their production is prohibited; otherwise, it is not. Sheikh al-Islam Ibn Taymiyyah held the view that it is not permissible to sell or tailor anything that is highly likely to be used to assist in a sin. The Permanent Committee issued a fatwa prohibiting the manufacturing, import, and sale of anything used in a forbidden manner, such as transparent or tight clothing. You must advise your mother about this, for ill-gotten wealth is impure, but there is no harm in eating her food and benefiting from her wealth because spending is permissible, and the prohibition concerns her alone.