I pronounce
Teresa /
Theresa as teh-REE-sa and it really bugs me because I prefer the eh / ay pronunciation much better, knowing all along it won't be pronounced like that where I live. Lately, I've been loving
Teresa with the nns Resa or Rese (long 'e' sound) so I'm coming to grips with it. ;-)
With Mother
Teresa (who I greatly admired), I automatically pronounce her name teh-RAY-sa because I've always heard it pronounced that way.
Like many names (mine included), there is no one correct way to pronounce
Teresa /
Theresa.