Wade, hon, I'm not sure you can straighten her out. Her doctors need to be clued into all the meds she's on/mixing/taking, which are almost certainly combining to make her sicker than she already is. It sounds like she very likely needs to be in the hospital for a few days while they get her meds straightened out and help her shed some of the water she's retaining. Sedatives and pain meds depress the cardiovascular system, which begins not to be able to pump off fluid effectively, and that's why the water retention happens. It's basically a form of drug-induced heart trouble.

Don't try and persuade her to do grass if she doesn't feel comfortable doing so. She's not really in her right mind to make any decisions right now.

Do you have a dad or a grandmother or a close trusted friend of your mom's who can gather up all her meds and get her to her doctor and tell him/her the straight story on how much you suspect she's taking? I gather this is some kind of non-cancerous (non-malignant, as you said) but very aggressive tumor nonetheless? On top of the tumor, which has affected her brain, there are the medicines, too. Bless your heart--and hers, too. I'm sorry you are having to endure this.