Brief Answer:
Please refer to the following suggestions...
Detailed Answer:
Hi, 
There are many reasons for such sudden 
knee pain.
- the most common is 
injury. Although your daughter does not remember to get her knee injured; it might had happened without being noticed. So, a physical examination of your child's knee is important for final evaluation. 
- usually, children at the age of your daughter do get such knee pain due to growth spurts. At the age, the growth rate of her bones, tendons, and muscles is high but does not happen at the same time.
Thus, the work of bones, tendons and muscles is not "correlated", leading to pain, commonly when walking/moving. Such pain remains until the age of 18 when the maturity of bones is achieved.
- another reason could be a sudden stretching of her lower 
limbs when trying to get out of bed, which has caused pain. 
I'd advise to give her 
paracetamol or 
ibuprofen for the pain and to apply warm clothing locally to relieve pain. You can apply 
analgesic cream containing menthol locally for the pain.
At last, I suggest to consult her 
pediatrician for further evaluation as it is needed to examine physically her knee.
Hope it answered to your query!
Feel free to ask me other questions you might at the next follow up! If you are satisfied with my answer, please close this thread and kindly rate my answer!
Thank you!
Dr.Alba