repeat ear/eye infections

[fjm]

Has she been tested for FIV and FeLV? It sounds as if she has been vaccinated against them, but no vaccine is 100% effective - it may be worth testing.

I would avoid the use of essential oils on cats - they can be very dangerous, and in my opinion too risky unless you really, really know what you are doing. Far better to ask your vet about preparations to discourage fleas, if using a topical treatment is contra-indicated. There are some safe ideas here http://everydayroots.com/flea-remedies-for-cats, although I don't know whether your cat would appreciate smelling of lemon!

There are lots of supplements sold as boosting the immune system, but I would look first at her diet - if that is right she should be getting everything she needs.

[booktigger]

L-Lysine is normally used as an immune booster, your vet would probably stock some.