I can imagine that many people in the USA would look at "Dea" and want to pronounce it to rhyme with either
Bea (which is normally pronounced "bee") or
Rhea (which is normally pronounced "REE-uh"), so I'm not surprised you aren't getting many people who have "DAY-uh" as their first guess. Unfortunately, it will be hard to find a spelling that will automatically give the pronunciation you want, because many people will now look at "Daya" and think it has to rhyme with
Maya and so be pronounced "DYE-uh". "Daea" might be your best bet for getting the pronunciation you are going for, but many people may think that one looks awkward. So you will just have to choose the spelling you think will be most appropriate, and know that there simply is not "perfect" spelling at this point in history for a name of that sound.