A 35-year-old woman from Bangalore with a 10-year history of systemic lupus erythematosus (SLE) presents with recurrent bacterial infections (Streptococcus pneumoniae, Haemophilus influenzae) despite adequate antibiotic therapy. Laboratory investigations reveal low serum C3 and C4 levels, positive anti-C1q antibodies, and evidence of immune complex deposition in the glomeruli on kidney biopsy. Which mechanism best explains her increased susceptibility to bacterial infections?