If you gave more details it might help find her a home -- why was she semi-retired? (did she have any medical issues?). You can also edit your title to include your location.
Since there are very few homes for retired horses, you could also find a retirement farm and board her there. A few people on this board run them; there is a big price range. If she doesn't need much care (that is, can be in a field w/o blankets etc) you would be able to board her at a place that charges at the low end.