Does two people being treated differently with medical problems be considered discrimination?

Hi I work a fulltime job I have been there for 18 years, I recently was on medical leave I had 2 surgeries and was off work for 2 1/2 months. when I got back I see a note posted that if anyone could spae some vacation time for another employee or would like to donate money to this employee? But they never did anything like that for me when I was off, and thenas of 2 weeks ago I fell at a store and was off for a week and a half and also my mom had a heart attack, after that week and a half I was told if I did not return within 14 days that I would no longer have a job, so I made doctor release me but I start physical therapy on Monday, Now that other person has to be off for 2 more weeks and they put another memo out if anyone is willing to donate their vacation time to her. How is this not dicrimination when if they are gonna ask for one should'nt they ask for another person also. Not just pick and choose who they do this for? Please help