I am sorry to hear she does not like it being touched.With a swollen face, there are a few possibilities to consider. First, as you alluded too, it could be an allergic reaction. Secondly, it could be a bacterial abscess infection. Lastly, and most unlikely due to her age, it could be a tumour.If it is an allergic reaction, a visit to your vet is warranted. You can give over the counter antihistiamines (such a 2.5 mg of cetirizine or 2 mg of chlorphenamine). However, these are much more useful at preventing issues. Once an allergic reaction has occured, it would be best for a dose a steroid from your vet. Check the bottle of piriteze to see if it contains either of the above active ingredients. If this is the 1 mg/ mL bottle, then you would need to give her 2.5 mL. But as I said before, this drug is best for preventing allergies, not stopping a reaction. Consulting with your local veterinarian would be the best course of action.In addition, since it seems to be uncomfortable to touch and she has been sleepy, I would be suspious that this could actually be a bacterial infection in the form of an abscess. Without physically seeing and feeling the sweling, I cannot be sure either way. If it is an abscess, it may need to be surgically lanced and she will need to prescribed medicines from your vet.