A 30-year-old woman at 34 weeks' gestation presents with new-onset hypertension (155/102 mm Hg), headache and visual disturbances. Urinalysis shows 3+ protein and reflex labs demonstrate platelets 85 × 10⁹/L and elevated AST/ALT. According to SOGC hypertensive disorders of pregnancy guidance, what is the most appropriate immediate management priority?