Sister-in-law's years of infertility drew mother's displeasure; one sentence at the birthday dinner table turned her face pale

Sister-in-law's years of infertility drew mother's displeasure. On her birthday, brother and sister-in-law came to dinner. Sister-in-law said one sentence, and her face turned pale
We often say an old saying: a harmonious family prospers in everything. Indeed, only when family members live in harmony and care for one another will the family thrive and life be happy and fulfilling. And I myself have a very deep personal understanding of this old saying. Because between my mother and my sister-in-law, there once existed some conflicts, and because of this the harmony of the whole family was affected.
My family is not large. My father passed away early, and only we two siblings and my mother lived together. After we grew up, my brother brought home a sister-in-law for me. She was kind and virtuous by nature, not only did she have a very good relationship with my brother, but her relationship with my mother was also quite good. Although our days were not very wealthy, the family was full of joy and harmony.
However, the one flaw in this perfection was that after my brother and sister-in-law had been married for several years, she still had not become pregnant. Although they sought treatment from many places, the results were not very ideal. At the very beginning, my mother showed no unusual behavior, but as time went on, she began to show a mood of displeasure. Every time she saw my sister-in-law, she would always bring this matter up, whether directly or indirectly. Toward this attitude of my mother's, my sister-in-law never offered any rebuttal; she would only give my mother an apologetic smile, as if she had done something she felt guilty about. Seeing this, I felt somewhat unable to bear it, so I secretly tried to persuade my mother to restrain her attitude from then on. However, not only did my mother not listen to my advice, she instead accused me of betraying the family and not being of one heart with her, which made me feel extremely helpless.
Not long afterward, it happened to be my mother's birthday. In order to bring the whole family together, my mother deliberately prepared a table full of dishes and told me to call my brother and sister-in-law. But when we had everything ready, my brother and sister-in-law arrived late. Because my mother had always harbored resentment over my sister-in-law's infertility, and on top of that their lateness, my mother was very displeased and kept complaining. But when she asked the reason for the lateness, a few words from my sister-in-law turned my mother's face pale, leaving her extremely embarrassed and unable to say a single word. It turned out that my sister-in-law had already become pregnant before this, and because she felt somewhat unwell, she had come late. However, my sister-in-law did not mind my mother's complaints toward her; she only gave a faint smile, as if nothing had ever happened.
Seeing the scene before me, my heart was instantly filled with mixed feelings and endless reflections. I was not only moved by my sister-in-law's behavior, but also displeased with my mother's actions. Without my sister-in-law's tolerance and magnanimity, how could the harmony and happiness of this family have been maintained?
(From a reader's submission. The images in this article are from the internet.)