I can't really add much to Jemma's post, just passing along hugs and prayers for your Mom's quick recovery.
My feeling is she has just had the bad luck to develop gall bladder problems, which can cause many of the symptoms your Mom is having. An underlying infection (UTI is a good call, as it can often "fly under the radar", causing general abdominal pain and a feeling of unwellness rather than classic burning upon urination).
Anxiety and depression can often occur after major surgery, which your Mom just had. I've had hip replacements and it takes a while for the anesthesia to completely leave your system, sometimes weeks or months. Some post-op pain meds, in some people, exacerbate depression.
Please keep us updated and let us know how she's doing!
A urinary tract infection will cause your mum to feel ill.
The metallic taste in her mouth is due to the congestion in her sinuses and throat. She needs to get a doctor to check her throat and needs to know about the sinus problem. Your mum may need an antibiotic if this is a bacterial infection.
If she is able to, try and get her to do steam inhalations - this will help to loosen up and clear the mucus. Avoid giving her milky drinks while she is unwell because milk encourages the formation of catarrh.
For a steam inhalation, pour a boiling kettleful of water into a bowl, taking care not to get scalded. Put some vick or olbas oil into the hot water. Get your mum to bend her head over the bowl and get her to cover head and the bowl with a towel and breathe in the steam through her nose and out through her mouth. If she can get her to do this 4 times a day for a duration of 10 minutes each time. If she is feeling very depressed, she may not want to do this, so don't force her. Putting some menthol oil or Vick on a hanky for her to sniff, can also help to unblock her congested sinuses, but not as good as the steam inhalation.
The nausea and loss of appetite may be due to gallbladder problems or a urinary problem - the ultrasound scan would show any problems in the gallbladder. It would also be a good idea to get an ultrasound scan done of your mum's kidneys to see if she has any kidney stones that were causing the urinary infection and her being unwell still.
Your mum needs to drink plenty of water. This will not only help flush out any bacteria in the urinary tract, but will also stop dehydration.
Has your mum had her ears, nose and throat checked for any infections?
Just give your light meals, nothing fried or heavily spiced. Soups are a good choice. Important thing is for her to drink, water, fruit juices, her favourite soup, jelly, ice-cream.
Once your mum's health improves, she will then not be so depressed.
Wishing her a speedy recover lots of strength for you to help your mum to get through this rough time.
Best wishes.