"Da ist ja meine Schöne."

Translation: There is my beauty.

[blargblargblarg]

So ja is used here as an interjection, without any effect to the sentence?

[christian]

It's a modal particle. You could translate it as "well" or "why".

Why, there she is, my beauty.

http://coerll.utexas.edu/gg/gr/mis_04.html