Mom 88 Yrs Old Has Had Copd For 4 Years,

Mom 88 yrs old has had copd for 4 years, oxygen level was set on 3, using only at night. On 4/11/16 she fell& needed hip replacement. Was put on 24/7 oxygen at that time. Last week, she was having more difficulty breathing, so visiting nurse set machine at 4. Is this ok or dangerous?