Sorry to hear of your loss-I think I too would just keep her for riding since this is the 2nd time for her. I think they do get depressed-I had a mare w/a stillbirth years ago,& another that lost an older foal just before I bought her-took her about a year before she lost that sad look in her eyes.
Here's Trixie now...she has been cleared by the vet and we decided to turn her out in the small paddock with the other 2 mares. They seem to have a close bond and I believe they will help her. Trying to get her back in tone...the loss of the foal in utero took a toll on her.