The full name for this deity is Papatuanuku, not just Papa. The word 'Papa' is also used to address ones father in Maori, although the sounds of the a's are elongated as with a macron over them. [noted -ed]
I see nothing wrong with the name, but seeing that I call my father "Papa" (and many languages use this as a familiar form of "father"), it seems somewhat odd.
It's like with the name "Kiefer" which means "jaw" in German. This will probably prevent most Germans from ever using the name Kiefer for their child - but does it mean that the name itself is bad, that it is a don't-use-it!-name? No, it doesn't. However, "Papa" does mean "dad" in more than just one language, and this makes it - of course - for many people more unusable than, for example, the name Kiefer, as you should also always consider where you live and if your daughter might have trouble with her name growing up in a country where Papa isn't a common first name. It is, because of everything the name implicates, very difficult for me to look at it objectively in order to say "I like this name" or "I don't find it appealing".