The reason I ask is because my friend started wearing one, next to her cross, so I was wondering if it was ok to wear one?
I don’t see why not. 
The geometrical shape known as the Star of David, though often associated with Judaism since the 1600s, has a long, transcultural history. It was a symbol of auspiciousness throughout much of Western (including Islamic) history. In India, it is called the “shatkona” (the “six-cornered”), has a very ancient history, and is associated with various Hindu manifestations of Divinity.
Maybe if more non-Jews had worn the Star of David in the 20th century, history would have turned out differently.
SD
Ryan,
I wear a crucifix on one chain and a Star of David (that has a small cross inside of it) on another. I purchased it at our local shrine. There is nothing wrong with wearing one; after all, Jesus was Jewish.
Now I have been approached on more than one occasion and questioned as to why I wear both, so tell your friend this may also happen to her. The tone of the questioners voice is what I use to judge my response. When it’s asked with sarcasm (this happened a few weeks ago after daily Mass), I simply reply that my crucifix reminds me of the sacrifice Jesus made for me and all mankind and the SoD is in honor of His heritage. Short, sweet and to the point. When asked with sincerity, I respond with a more in-depth explanation (which has led to some great discussions).
Peace and Godspeed.
I can’t recall exactly where, but I know I’ve seen a 6-pointed, star-shaped, stained-glass window above the altar in a veeery old Catholic church.
The six-pointed star is also known as the Star of Damascus and is often seen on military swords. Sword craftsmen used two triangles joined together as a sign of their sword making guild which became know as theStar of Damascus. This symbol means the sword was fashioned with Damascus steel.
Greetings Church
As Catholics, we have Jewish roots. A priest pointed out that we are truly “Completed Jews”. I love this concept so much that several years ago, my son had a beautiful gold Star of David made for me with a Cross set right in the middle of it. It is beautiful and I really cherish it.
can a catholic wear the star of David
Here is a Catholic religious order for older women in Mexico.
Eudist Servants of the Eleventh Hour
The Sisters are wearing a cross with the David Star on.