Hi. She has no interest in food at all which is unusual for her as she's usually very good at eating. There's been no vomiting etc as above. I think she is possibly drinking more than usual. Not sure about urination and faeces. She is going out into the garden but I've not managed to observe her doing anything as yet.
To complicate matters, we get very concerned for cats who go off their food (and as I noted before this is getting worrying) because cats were not well designed for the anorexic lifestyle. When they are off their food, body fat is broken down and released into the blood stream, causing their liver distress (ie. hepatic lipidosis) that can make getting them better even more difficult for us.
Now if she is turning away from food, then it her signs could include nausea despite not showing any vomiting (often nauseous cats go off their food rather then eat/vomit like a dog would). That said, this can be GI based but it can also be associated with systemic diseases that have an associated nausea.
To rule out nausea as an anorexia differential, you can try her on antacid therapy. There are a number of antacids that are available over the counter and pet friendly. I would advise only treating with one, but the two I tend to recommend are Pepcid (http://www.petplace.com/drug-library/famotidine-pepcid/page1.aspx) or Zantac (http://www.petplace.com/drug-library/ranitidine-hcl-zantac/page1.asp). This medication of course shouldn’t be given without consulting your vet if she does have any pre-existing conditions or is on any other medications. Ideally, it should be given about 30 minutes before food to easy her upset stomach.
As well, you will want to try and see if you can get her eating (as I see you have been). Favourite foods are allowed or you can tempt her with a light/easily digestible diet. Examples of this would be boiled chicken, scrambled eggs (made with water and not milk), meat baby food (do avoid the ones with garlic powder in the ingredients) or there are also veterinary prescription diets that can be used here (ie Hill’s I/D or Royal Canin’s sensitivity.)
Further to this, if she has been off her food for a while and if tempting doesn’t work, then we do have to consider initiating syringe feeds to get food into her. In that case, you may want to try Hill's A/D (http://www.hillspet.com/products/pd-feline-ad-caninefeline-critical-care-canned.html) from your local vet. This is a critical care diet that is comes as a soft, palatable pate. It is calorically dense, so a little goes a long way nutrition-wise and this could just help get some more calories into her even if we can’t get a huge volume of food in. As well, for syringing food, you can use the animal version of Ensure (balanced for animals dietary requirements) called Clinicare Canine/Feline Liquid Diet (http://www.abbottanimalhealth.com/veterinary-professionals/products/nutritionals.html) . It is actually by the same people who make Ensure, but is formulated to meet out pet's dietary needs. Your vet should be able to order it for you but it is available without a prescription (Amazon stock it as well). They also make one specifically for older cats with kidney troubles, and this could be an alternative for an older cat. This way it would a means of getting food, staving off hepatic lipidosis, and buying you time to uncover the reason for her anorexia.
On top off all of this, you do need to keep an eye on her water intake. Even though it sounds like she may be drinking more, you do want to check her hydration now To check her hydration status to make sure she is not becoming dehydrated there are a few things we can test at home. One is whether the eyes appear sunken, if the gums are tacky instead of wet/moist, and whether the pet has a "skin tent" when you lift the skin. To see how to check these parameters for dehydration, you can find a wee video on this (http://www.ehow.com/video_12232503_dog-dehydrated.html). They use a big dog but it makes it easier to see and the principles are exactly the same. If you are seeing any signs of dehydration already, then you do want to have your kitty seen by her vet before this gets out of control for her.
In regards to what you can do to help stave off dehydration at home (though do note that if she is already then she will likely need more the oral rehydration), encourage her to drink but offering fresh water or even low-sodium chicken broth. As well, wet foods (as mentioned above) are 35% water, so getting her to eat will help us deal with water intake as well. If she isn't amenable to drinking, you may wish to offer unflavored pedialyte via syringe feeding. While we cannot do this if they are vomiting, it may be an option for this situation. A typical maintenance rate for hydration in an animal 48mls per kilogram of her body weight a day. If you do give syringe pedialyte, this should obviously be divided up into multiple offerings through the day rather then all at once. This value will give you the total she needs for the day and is a good starting point to give you an idea of her daily requirement. If she does vomit when you give pedialyte, I would discontinue this as a therapy. (since we don’t want Heidi vomiting because of our intervention).
I hope this information is helpful.
If you need any additional information, do not hesitate to ask!