Hi,
The rash you describe is certainly evident from the photo. The entire underside appears erythematous. There are a number of possible causes. The first thing to do is to rule out parasites - although this looks more like an allergic dermatitis, it is prudent to apply an antiparasitic spot-on to rule out sarcoptic mange (scabies), an intensely itchy parasitic condition normall contracted from lying on ground where a mangy fox has been recently.
You can give an over the counter antihistamine tablet such as Piriton. This may take away some of the inflammation. It is safe to give a childrens piriton tablet twice a day, even long term. However, with severe allergies this is seldom enough.
Other possible causes are contact dermatitis (a reaction to a chemical the dog has encountered, perhaps a carpet cleaner or washing detergent). Think hard whether anything has changed in Kiki's environment lately. Otherwise you would be looking at an allergy - either to an ingredient in the food, or something in the environment such as a certain type of grass.
I would try antihistamines, rule out parasites with a veterinary spot-on treatment, and if the rash is still there, consider a strict dietary trial with a hypoallergenic diet preferably, at the very least boiled rice and chicken, for 4-6wks.
Severe environmental allergies (atopy) can sometimes only be controlled effectively with corticosteroids (prednisolone).
Good luck.