[MMM]

I have the opposite reaction. If you are getting a permanent seal on your body in dedication to your legacy of having a Japanese middle name, I would make damn sure it was written the way it is intended, and not just toss はる in a dictionary and add 子　to it.

張る子 would be kind of a funny name.

はるこ is your safest bet, as it is "meaning-free", but no one could tell you that you were wrong.