Peach Blosson Luck is a love potion, or something that means attracting love and romance.

In the story, the mother believes that the mirror which was placed under the bed of the daughter would deflect the love of her marriage (and the romance in the bed) away, and it is considered bad luck. When she placed a mirror above the bed to reverse the effects of the this, she believed that it would bring "peach blossom luck" which is the love luck, and that way she would provide such needed love for her daughter to procreate a male child, and give her a grandson.