Susanna is a smart young woman and I think she felt a need to use her brain and talents rather than just sit around. I think she had a real sense of accomplishment and satisfaction in representing her father's interests in his investment. She also knows that while her mother needs time to grieve that the household needs to be taken care of and so she assumes the responsibility for it, though she, at the same time, is aware that her mother needs to snap out of her grief for her own sake. In an attempt to revive her mother, she urges her to come back into the garden, to go out and collect rose hips ect.
As to her chances for marriage--hard to say. The author does not bring young men into Susanna's life for us to assess. Nevertheless, this is a girl with a head on her shoulders, she's healthy, she's a good housekeeper, she is young and pretty, and she is wealthy. I suspect there will be bees buzzing around--but who knows how good a man he will be? Which of those attributes would be MOST attractive might make the difference.