Iron is an important part of the immune system, and if deficient, she could very well be susceptible to infections. First prize would be to get her out of the environment where she is constantly bombarded with numerous viruses and bacteria.
A babies immune system is very immature between the ages of 6 and 36 months, and until she reaches a stage of immune maturity she could get sick quite often. I unfortunately do not have much faith in the multitude “immune boosting “ products available on the shelves of supermarkets and pharmacies.