My mom thinks she spends money better when it's the opposite and she blows through it like crazy.

I have 600 a month that I can use since saving up before having to stop working. My SO brings in 1600 a month and my mom makes 750 with her disability. My rent and bills come out to 1900. My mom sends money to a church organization every month. All in all it leaves us about 800 for the month for food, gas, extras and my mom and SO smoke cigs. 

When I have control of the money I can feed a house of 5 for 100 a week. My mom will spend like 200 on junk food so I try and sneak away to do the grocery shopping. My SO works 40 minutes away and we have a large truck that is shit on gas. So that's another 100 a week. Basically we have just enough to get by, but my mom whines she doesn't have money for herself when we pay for whatever she needs - hair dye, extra clothes, coffee, cigs etc. For the past 7 months me and her split the rent which left me completely broke and her with 100 after her church donation and my SO would pay for whatever else we needed and food. She has been on a tangent that she wants everything split 3 ways because then she'll have more money left over and my SO wouldn't have control over it because she thinks we should have 400 left over every month to play with (which makes no sense) and says he's lying about gas and it should only cost him ten dollars a week to get to work and back. I just laughed. She has been living rent free for 18 years until she moved in with me because my family sold the family house she was staying in and I paid her bills back then. She has no idea how to manage money. I just get super angry when she blows through her extra cash on top of us buying what she wants, then gets pissed when it's a couple days to pay day and we can't go shopping. Almost slapped her. I told her to just give me 500 a month, it gives her extra - but she cannot ask us for extras at this point on. She's still bitching about it but I don't care. It's either that or move out, I guarantee a roommate who isn't her daughter will be far less nice.