My 12 month old daughter's IgA and IgG levels are low. Is this serious and what are the treatments?

See an immunologist. The levels might not be low for her age, normal levels depend on specific age. If they are truly low, it might be a transient deficiency that could resolve with time, or she may have an immunodeficiency.
It depends. The most important thing is your daughter's history. If she is healthy, the levels are probably low because her immune system is a little slow developing. If she is sick more than the average child (3-8 infections per year) or has unusually severe infections, she may have a clinical immune deficiency. If so, she can be treated with Immune Globulin and/or prophylactic antibiotics. See immunologist.