There is nothing wrong with manufacturing and sewing clothes, whether they are abayahs or anything else, so long as they are not things that may be used to help do haraam things, such as clothes in which women make a wanton display of themselves and show off their beauty in front of non-mahram men, because Allaah says (interpretation of the meaning):
“Help you one another in Al‑Birr and At‑Taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression. And fear Allaah. Verily, Allaah is Severe in punishment”
But if the clothes are those that may be used for good or for bad purposes, and some women may wear them in the house whereas others may wear them outside, if it is known what the purchaser will do, then they may be made for and sold to those who it is known intend to use them for good purposes, not bad. But if it is not known what the purchaser or the one who asks to have them made will do with them, then the manufacturer or seller should act on the basis of what he thinks most likely to be the case. If he thinks it most likely that the purchaser will use them for haraam purposes, then it is haraam for him to make them. But if he thinks it most likely that he will use them for permissible purposes, then there is nothing wrong with making them.
Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him) said in Sharh al-‘Umdah (4/386): All clothing that one thinks it most likely will be used for sinful purposes, it is not permissible to sell it to or sew it for one who will use it for sinful and wrongful purposes. End quote.
It says in Fataawa al-Lajnah al-Daa’imah (13/109): Everything that will be used in haraam ways or it is thought most likely that it will be used in such ways, it is haraam to manufacture it, import it, sell it and distribute it among the Muslims. That includes what many women do nowadays – may Allaah guide them – wearing see-though, tight and short clothes. All of that may be summed up as showing their charms and beauty and showing the shape of women’s limbs before non-mahram men. End quote.
You should advise your mother and explain to her the details mentioned above. Tell her that the money that comes from making something that is haraam is impure wealth in which there is no goodness or blessing. She should limit herself to making that which is permissible according to sharee’ah. Hopefully she will respond to that, but if she persists in making haraam things, there is no sin on you if you eat from her food and benefit from her wealth, because you are taking the wealth in a permissible way, which is her spending on you. The prohibition on this wealth has no connection to you, rather it has to do with your mother only, because she is the one who is acquiring it in a haraam way. But it should be noted that her wealth contains both halaal and haraam; it is not all haraam. This also supports the fact that it is permissible for you to benefit from this wealth.
And Allaah knows best.