She is determined, she is independent and she is on her own schedule..
Stubborn people are people that are not willing, will not try and are afraid.. That does not sound like your daughter.
She is not stubborn. Please, quit using that term and never use it in front of her.. If you tag her, she will believe it and behave like that
She sounds like she is on her on schedule and is fine,
She is talking if you have heard the words you stated.
Even if she does need some assistance in the future, it will be fine.
Here are the things you can do.
Continue to speak around her. It will feel strange, but speak about whatever you are doing.
"It is time for me to clean the kitchen. I will start filling the sink with water and add some soap. Here is my sponge, I will be wiping off the counters and the table. now I will wipe off all ot the appliances. The refrigerator, the stove, the dishwasher. "
"I need to take the clothes to the laundry room. The laundry room is the room with the washing machine and the dryer."
"I am putting the white clothes in the machine. Oops, these are blue, they will go in the dark pile. " P{lease hand me the shirt next to your feet. Thank you for your help. "
Of course she will not understand everything.. but the sounds, the language.. it will make connections for you..
Even in the car.. She may not be able to see out the window like you, but you can still talk about what you see. "There is the grocery store. We buy our food there. "
"There is Target, they have the red carts."
Keep a record of her meals. Jot down what she does seem to eat, what she has trouble eating. Maybe you will see a pattern.
To get her to eat or try things.. As you eat, comment. "Yummy, these carrots are sweet, May I share one with you?"
"Oooh, your bread looks good, May I have a piece of your bread? Thank you, nice sharing! Yummy, it is tastes good. "
My niece was and still is just a tiny person. She does not have a huge appetite, but she is VERY active.. a Cheerleader, plays soccer.. But she is petite.. I noticed her half sister is the same way..
So continue to stay alert and make notes, but know that she still falls in that normal scale.