Finding Flower Seeds on Harvest Moon: A Wonderful Life is the key to Celia’s Heart
You can gauge the success of your actions by checking out the diary that is on her bed from time to time. This diary will let you know how she feels. If it is red then you are doing well.
Offering Celia flowers every day and purchasing seeds from her often is the first step to sealing the deal. If you give Celia the Goddess Drop located near Vesta's every day then within one season she will be ready to accept your marriage proposal. Once you have four hearts from Cecilia you can invest in some bird seed which will come with a blue feather. Take that blue feather and give in to Celia to let her know you are ready to marry her.