O-lan is certainly a good person, to say the least.  She is kind, considerate, self-sacrificing and hard working.  To the best of my knowledge, there is not one incident in the novel that tells of a selfish or thoughtless side of O-lan; she even fails to really protest when she gives over the jewels she has treasured for so long.  There are many passages and quotes that reveal O-lan's generous and giving characteristics.

...The woman, when he had gone in the morning, took the bamboo rake and a length of rope and with these she roamed the countryside, reaping here a bit of grass and there a twig or a handful of leaves, returning at noon with enough to cook the dinner.  It pleased the man that they need buy no more fuel.

In the afternoon she took a hoe and a basket and with these upon her shoulder she went to the main road leading into the city...and there she picked the droppings from the animals and carried it home and piled the manure in the dooryard for fertilizer for the fields. These things she did without a word and without being commanded to do them.  And when the end of the day came she did not rest herself until the ox had been fed in the kitchen and until she had dipped water to hold to its muzzle to let it drink what it would.

Even when O-lan was on her deathbed, she thought of those around her and referred to herself as a slave, taking pride only in her role as a mother.

"And has everyone wine?  And is the sweet rice dish in the middle of the feast very hot and have they put full measure of lard and sugar into it and the eight fruits?"

When he assured her that everything was as she wished it, she was content and lay listening.

...Strength passed from O-lan and she grew weary and faint and she called to her the two who had been wed that day and she said,

"Now I am content and this thing in me may do as it will.  My son, look to your father and your grandfather, and my daughter, look to your husband and your husband's father and his grandfather and the poor fool in the court, there she is.  And you have no duty to any other."

..."Well, and if I am ugly, still I have borne a son; although I am but a slave there is a son in my house."  And again she said, suddenly, "How can that one feed him and care for him as I do? Beauty will not bear a man sons!"