@Sux2buthen I'm so sorry that you and your family are going through this, I have experienced it from both sides, and it is terrible. The most obvious infection that can cause horrendous confusion/delirium is a urine infection. Your DM could have one alongside Covid, and if she has a catheter, or has to wear adult pads, she is very likely to get urine infections. Another "big" cause of confusion can be dehydration, and urine infections and dehydration, often go together. If the dehydration gets too bad then the patient has to be hospitalised to make sure that - paradoxically - they don't get rehydrated too quickly, which can also cause serious problems.
If your DM is not on antibiotics for a urine infection it sounds like it should definitely be considered and checked for. If your DM isn't catheterised, but is delirious, then it will probably be almost impossible for any of you to get a urine sample - you would probably need either a community nurse, or one in the hospital, to do a quick in and out catheterisation, to get a urine sample from her bladder. Even if a sample can be got, there isn't time to wait for the result, your DM would need to be put on an antibiotic straight away. If a Dr - who really must make a home visit this time (I know) thinks her symptoms are bad enough, then she may need to be in hospital to have intravenous antibiotics.
If she is delirious for any reason, then she isn't up to making decisions in her own best interest, for now, so her next of kin - your DDad? - or you, or your brother, may unfortunately need to push for her hospitalisation at the moment. As soon as she is better you can all - or maybe just you and your brother if your DDad would find it too hard - gently but firmly, explain to her that she really does need carers at home, or to go into a nursing home; as a similar sounding woman to your mother, I know which I would choose. Carers coming in can be annoying for all who live there, but hopefully it would be preferable to your DM going into a home.
I know that the Health Service is on it's knees, but did the hospital really send her home without taking a urine sample, and giving her antibiotics? The paramedics who went to her house today, could check her temperature, her blood pressure, her Oxygen levels, and even give her a heart trace if they thought it was necessary (if they didn't do the first 3 then they are incompetent - but they will have done them), but presumably they couldnt take a urine test, and even if they did, it could show up certain things that can be indicators, but not what infection your DM might have.
I was in hospital last year with a very bad urine infection, that they didn't treat for ages because all my vital signs were fine, even though I was in a lot of pain, and they didn't believe my pain at first because all of my initial readings looked good. It took another 7 to 8 hours until I got a massive rise in temperature, and my other signs started dropping.I was in hospital for days before my intravenous antibiotics started to get the better of my infection.
Despite all that I have said here, please don't panic @Sux2buthen, that was me, and then, and there. Your DM could, and hopefully is no-where near as bad as me, you don't even know whether she has a urine infection or not. I just don't want you or anyone else to think it is "just a urine infection", as with vunerable people of any sort (and unfortunately some otherwise very healthy ones) untreated urine infections can lead to Kidneys packing up, and or Sepsis, so if there is any chance your DM does have one, it must be treated.