you can pick any one you like then, if you haven't been given kanji already
in all of these 子 = child so i'll just tell you the others
春子 = spring (as in the season)
はる子 = this is hiragana so no meaning, personally wouldn't choose this one
晴子 = clear up/clear
治子 = reign; be at peace; calm down; subdue; quell; govt; cure; heal; rule; conserve
there are others that are not regular/common and Japanese might find hard to read correctly such as 美子 (the first character means beautiful but to read it is はる, while it is a documented reading of the character, would be very strange to Japanese from my understanding. i'm sure nagoyankee can confirm that. there is nothing wrong with it though, i know of a child called 青空 which would normally be read あおぞら but he is actually せいき so
at the end of the day it is your choice. copy and past はる into this page:
WWWJDIC: Kanji Selection and it will show you the characters that have that pronunciation.
you could also make the name 3 characters は・る・こ so feel free to chuck those sounds into the kanji search engine on that site and come up with a name you like.