what does bella una mean?

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More likely the phrase you ask about is "bella luna". That would mean the beautiful moon.

I don't know about Judeo-Spanish specifically, but it could perhaps mean 'beautiful one' (cf. definition of una). I think it is safe to assume bella means 'beautiful', so it's just really a question of whether una can mean 'mother' in this variety of Spanish.

There is a pretty extensive bibliography of Judeo-Spanish on jewish-languages.org. Perhaps if you track down the dictionaries there from a local library using WorldCat and look up the two words in question, you could get a more complete and accurate answer.