MIL moved in several years ago. Over time she helps very little and I feel like she wants to be waited on. Suggestions?

When your wife asks, "What do you want me to do?", tell her you want her mother to move out because she watches tv all day, lies, doesn't help, and is a big manipulator in general. Having an in law living with you for several years is more than enough and it sounds like NOW is the time for her to move out. She can go into Assisted Living now, and you and your wife can look into the various options available to her, based on her income, etc.

Good luck having a heart to heart talk with your wife about what YOU want!

How severe is her arthritis and depression? Each of those conditions can be very painful and debilitating. Sitting in the house, even if it is her own choice, and not having communication and interaction with other people can be a signal that something is not right. Before, I wrote it off as her being lazy or manipulative, I'd rule out actual medical reasons, like pain, depression, dementia, etc. If you rule those out, then, maybe, you and your wife can discuss some ways to get her up and about. What about offering to pay her for certain duties, like dusting, laundry, etc. ? Maybe, she needs a motivating force.

The reason I always encourage family members to explore reasons behind a LO's refusal to get out of bed, bathe, do laundry, help with dishes, etc. is that my LO started out that way. I was beyond upset about it. I consulted with healthcare professionals who told me they thought she was spoiled and lazy! But, that's not the case. It turned out that she was suffering from dementia (having mini strokes) and her limbs might have been capable of doing things, but, her brain was not able to tell the limbs what to do. I wish that I had known all along, but, hindsight is 20/20. People can be suffering in silence and not know how to verbalize that something is wrong with them.

When you say that she has been a "game player", do you mean that she does things like pits one family member against the other?

How did she come to live with you? What sort of agreement was there before she moved in? Or was it a sudden emergency and it just sort of happened?

Does your wife know that you are unhappy with this arrangement? It sounds like she has no reason to want to change the arrangement, or feels no power to do so. Did she and her mom have a good relationship before?

What alternative living arrangements have been looked at? Where are mom's dollars being spent? At the very least, she should be paying for room and board. And for respite care so that you and your wife can either get away or have some privacy.

Make a list of the things you expect her to do as a member of your household and also list the consequences if she does not do them.

Present it to her with your wife.

You could give her the option of choosing 3-4 things on the list.

But first you need to have a realistic assessment of her abilities. Where does she have arthritis? What can she manage to do?

If she is watching TV all day, she could fold the laundry while she watches it. You likely would have to carry the basket to and from her. But if the arthritis is in her hands, that may not be an option.

If washing the dishes is too much for her, standing may be painful, what about having her set the table? Could she also clear the table of lighter dishes?

Can she scrub the spuds and peel them?

What would be the consequence if she does not help in some manner with meal prep and clean up?

I once told someone who would pray over a meal I prepared, but never thanked me as cook, that he was no longer welcome to eat food I prepared. And you know what, I was thanked every meal after that one. Are you perhaps feeling used and abused? Would a simple thank you for all your effort help to alleviate the situation?

How is she manipulative and what does she lie about?

Pjmax
I get it that your MIL is getting on your last nerve but what do you want her to do? The MIL I mean.
What has she stopped doing that she used to do? Make a list for yourself and your wife.
Does she pay her way? Pay room and board? If you were to run through the IADLS and ADLS with her in mind, how would she do? After all she is well on her way to advanced age. She has lived past the average age for women in the US so it is not unrealistic to expect her to slow down.
Does she clean her own area? Does she do her own laundry? Pay her bills? Drive still?
If the answer is none of that then you need a care contract with her. She needs to appoint your wife and yourself as DPOA. Perhaps she already has.
What would she say if you asked her for a favor? Asked her to fold the laundry? Have you ever said “MIL would you help me with dinner?” Or ‘would you clear the table tonight?” Are you expecting her to initiate on her own?
Its awkward for you because it’s not your mother. I understand that. But if you haven’t already, take some initiative to advance your case.
Ask your wife to ask her mom for help to see if she’s able. Since you are with her more, you will probably notice her decline more or earlier than your wife.
Take a look at confabulation. She may have some mental decline.
I think many elders are depressed. It’s the end of life. You may be a bit depressed yourself knowing you are in this position of potential caretaker. At the least your MIL needs a good physical and a dialogue needs to begin on what plans are in place for her ( and your) future. Perhaps it’s time to look at ALF? Or a round of physical therapy.
Many many people watch tv all day. Maybe there is a senior center nearby where she can watch with people her own age or play games. Would you be willing to take her to explore those options?
I applaud you for coming on this site looking for answers. After you’ve done a bit of research you may have a better idea of what your wife could do and not feel petty about asking. You feel the decline. You are thinking it’s willfull. You could be right but I suspect there is more to be investigated before you let it cause you and your wife problems with one another. Dementia is very subtle but it progresses. Welcome to the forum.

Time for you to set your boundaries with your mother, she is getting away with this because you allow it. It is you who is making you "stuck", not your mother.

Sit down with her, tell her what is expected of her, stop waiting on her. Say what you mean and mean what you say.