cold and flu advice needed

hi my wife was diagnosed with diabetic 2 in 2013 , what we have noticed is that she keeps getting colds and flu allthough she has had the flu jab , my wife is aloud to take certain meds for her cold but is there anything you can suggest for her immune system , when she goes out she does wrap up and we try and keep her warm at home but she is getting cold systoms around every 2 or 3 weeks thanks

thanks for your replys , my wife has several health issues including mental health she is taking meds for this , our dr has said that she can take hot a hot lemon drink that contains paracetamol a bit like lemsip and she can have vapour rub as well , my wifes sugar levels are very good as she is on metformin once a day , and she has to take pain killers as well upto four times a day , allthough she drinks plenty she also gets bunged up and not being able to open her bowels every day , my wife usally goes onto antibotics as since she was diagnonsed with diabetic she gets chest infections , and i was woundering if there was anything that she could take to help her immune system thanks