Theory:

     The bird wouldn’t sing a song and he wouldn’t eat a thing. The Princess was a little anxious at this, and asked her sisters what they thought about it.

     “You must be firm,” they said.

     “But if he won’t eat, he’ll die,” she answered.

     “That would be very ungrateful of him,” they said. “He must know that you’re only thinking of his own good. If he’s obstinate and dies it’ll serve him right and you’ll be well rid of him.”
 
     September didn’t see how that was going to do her very much good, but they were eight to one and all older than she, so she said nothing.

     “Perhaps he’ll have got used to his cage by tomorrow,” she said.
Explanation:
 
The bird would not sing or eat anything. The Princess was concerned by the bird's refusal to cooperate. As a result, she sought guidance from her sisters. September's sisters advised her to stick to her decision. The Princess added that if the bird did not eat, he would die.
 
The princesses had thought the bird's lack of cooperation was disrespectful. They also said that he made no effort to comprehend September's worry for him. They also said that if he died as a result of his stubbornness, he deserved it. In exchange, the Princess may even be able to get rid of the selfish bird.
 
September, on the other hand, was unconvinced by their idea. Their counsel didn't seem to be particularly helpful to her. But she couldn't say anything since she was outnumbered eight to one. Furthermore, they were all older than she was.
 
September worried if he would be able to get adjusted to his cage by the next day.
 
Meanings of difficult words from the paragraphs:
 
S.No
Words
Meanings
1
ObstinateStubborn
Reference:
National Council of Educational Research and Training (2008). It so happened. Princess September - Somerset Maugham (pp. 34 - 44). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.