It happens in a lot of places. For a lot of districts it is way more challenging to find a good sub or associate as opposed to a FT teacher (as has been mentioned here a lot of El Ed positions get 100s of applicants in good districts). When you are a good sub, unfortunately some districts don't want to hire you as a FT teacher because they know it will be hard to replace you.
The other thing that has been thrown out in this thread that I would caution your wife on is continuing ed. While getting a reading endorsement would definitely benefit her, getting a master's degree or grad credits will make her more expensive for a school, which in many places is seen as a negative.
Good luck to her!
I guess it looks to be a 50-50 prop then. Some schools it's positive, some negative. Didn't know it was a negative before this.