Thank you for your question.
I am Dr. Su S. and I will try my best to help you.
I am sorry for her symptoms.
As she does not have fever, no difficulty in breathing & taking feeds well, there may not be an infection but you need to watch.
You need to take some precautions.
Please avoid contact of baby with her sister.
You need to wash hands after caring her sister.
If she develops fever, cough, refusal to feed, she will need an examination by doctor.
If you feel her nose is congested, you can use nasal saline drop.
I hope this information will be helpful.
If you have any query, please feel free to ask.
If you are happy with my answer please click on the Excellent/Good rating.
Wish her healthy life.