Oh man. Look this might be a bit scary for mum, but would she consider a temporary nasal tube to help her with nutrition? You can run an automatic pump for a slow drip so she doesn’t have to worry about mouth pain or remembering to sip.

I get the sense that she’s not a fan of sweets but Ensure does come in a neutral flavour that could be mixed into coffee or soups. MCT oil is basically a medium chain coconut oil that may help with weight gain (but may have uncomfortable or embarrassing solids effects, I haven’t tried it).

She may need a review on her mouth pain, a check on why it’s not resolving and if it can be managed.

I’m so sorry that everything is falling on your shoulders and your old man won’t step up. I wonder if perhaps there could be a home carer to assist with the soup and reminding her to eat. (Or to make it with her if she insists on cooking.)