Mestra (Μήστρα) was the daughter of King Erysichthon — cursed by Demeter with insatiable hunger. She was given by Poseidon the power to shape-shift, and her father sold her over and over to buy food; each time she returned to him in a new form.
Featured in Ovid's Metamorphoses Book 8.
Mestra 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 Mestra reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.