Agustina is from the Spanish Agustina — feminine of Agustín (Augustine) — from the Latin Augustus (venerable, majestic). Agustina de Aragón (Agustina Saragossa Doménech, 1786-1857) was a Spanish heroine of the Peninsular War (Spanish War of Independence) against Napoleon — widely considered one of the symbols of Spanish resistance.
Agustina does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Agustina reduce to 2, The Peacemaker. This is a traditional interpretive system, not a factual claim about the name.