I don't like
Mildred enough to use, but it has a great meaning and I don't mind the sound of it. I've never heard anyone consider it for a child outside of this board, and I've only met one bearer ever: she would have been born around 1910 and went by her middle name.
Millicent reminds me of millipedes and
Millicent Bulstrode. Milbrey is interesting, but not that appealing. Milbrow/Milbrough/Milborough seems to have had a fair bit of Victorian usage here in the UK, and I like that better: if it were a passed-down family name I'd definitely consider using it.