My 3 year old daughter gets ear infection frequently. what can i do to improve her immunity?

There are options: A lot of this answer depends on how frequent "frequently" is, and the type and degree of infection. Assuming this is middle ear infection (otitis media), up to a couple of infections a year is not uncommon and probably does not warrant further therapy except acute treatment. More than 3 in 6 months may warrant tympanostomy tubes. Adequate rest is the most important modifiable factor for immunity.

Antibiotics/tubes: 5-6 infections in a single year is an absolute indication for tympanostomy tubes to prevent hearing loss (associated with acute infection/chronic fluid). If she is having 2-3/year for the past several years, it is also reasonable to consider tubes. Further, if she has a documented "chronic infection" or fluid with hearing loss for 3 months, she should be evaluated for tubes by your local ent.

See below: For children experiencing frequent ear infections, avoidance of exposure to tobacco smoke, adequate immunizations against pneumococcus and influenza, and utilizing small sized babycare setting instead of large daycare would be advised. Tympanostomy tube insertion should also be considered if middle ear effusion persists between bouts of infections.