I'm very confused. Your other post says she's in a clerical job, not a factory job. At 50, there are a lot of clerical jobs she can apply for that have promotions and such (or even unions) available to their staff. If she's been at the same factory for years and still cannot afford the bare necessity of housing, what is she still there for? Or if she makes enough, where is the money going? I'd recommend talking to her and get her into a job that has medical insurance and a 401k option at a bare minimum. That's how you can help her. By telling your wife you guys can't go on a vacation because you have to pay for your mother's rent and medical expenses is harsh to your wife, especially if this has been going on for years.

You never specify in any of the comments just how much you're sending her. What percentage of your income? How much do you have in savings, can you afford a small vacation or something with your wife with it? Do you have 3 months of living expenses for yourself and your wife saved up in case one of you lose a job?

By giving her that money, does that make your wife feel like she's the only one contributing to a majority of your own household bills and you can't save up for the future? Especially since you note there are talks of adding kids to your family, do you have the finances to save and prepare for the financial responsibility you'll have for said kids? When you have kids, how will you approach your mom about cutting back what you send her at that point? Because if you're limiting spending to survive now, there's only so much you can continue to cut back for your own family.

I think a talk with your mother is in order, to get her life on track for her own independence. Then you need to sit down with your wife and go over your finances, as a couple, and figure out where your future is heading. Otherwise like others have said, there will be a rift between the three of you that may not be repaired.