Is It Normal For Sodium Levels To Drop Over Several Days While On IV Sodium In The Hospital?

My best friend is in the hospital for low sodium and a UTI.They treated the UTI and just has to get her low sodium back up. On April 27th in the morning it was 129. The next 2 blood tests they did it dropped to 128. The last blood test done at 1 am it dropped to 125. They have her on sodium ivs. Is this normal? She has been in the hospital almost 2 weeks. I am starting to get concerned.