Saint Mildburh (d. c. 715) was the Anglo-Saxon abbess of Wenlock Priory in Shropshire — sister of Saints Mildred and Mildgyth, granddaughter of King Penda of Mercia.
Famous in medieval England for miraculous healing.
Mildburh 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 Mildburh reduce to 6, The Nurturer. This is a traditional interpretive system, not a factual claim about the name.