Agree that they tend to adjust pretty well to eyesight issues, but I completely understand getting a bit emotional about your senior's health!
For your sake, get in the habit of keeping a hand on her and talking when you're working near/with her, just so she knows where you are at all times. I know several fully blind horses who fare perfectly fine, the handlers just stick to a routine for comfort - the horses know their stalls, know the exact walk to their pasture, know that pasture's fence lines, and the fence lines are pipe & rail or board fences (not wire) so they have safe, easily felt borders.
~Reserved Cash, 2011 AQHA gelding~
~Lark, 20-something Arabian mare~