Using Oxygen

Hello,My sister had a wedge biopsy on her left lung....The doc said she would be in hospital just overnight.   He also said she would be a little sore from surgery at incision sites.  Well, she was discharged from hospital today, Saturday and has been in a lot of pain.  Also, she has been on oxygen because her numbers are low.  She also had to be discharged with it.    Is it normal to need oxygen after a wedge biopsy? And, how long do you think she will need it?  Thank you and God Bless.Danielle