backing up 3rd base

Question
My wife Vicki asked this question because I'm coaching the team and I have the pitcher backing up a throw on a play at 3rd and home only. I was taught this my whole life but she insists it is different for girls softball. Once again, I only have her do this for 3rd and home because there is no one else to back up those throws.
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Followup To

Question -
Who's responsibility is it to back up first and third base?  My daughter is playing little league 9/10 allstars. She is a pitcher and they have her leaving the mound to cover infield positions during a play - is that correct.  Last year during the tournaments, the pitchers generally stayed withing the pitching cirle because in little league, if the pitcher has the ball within the circle play stops.  any help would be great.

Answer -
It depends.  In college the pitcher backed up the catcher when a play was coming come from the outfield because there is no need for the pitcher in a relay to home.  The pitcher can back up someone if she is a few steps away from the circle.  Outfielders back up infield positions.  For example, if the ball is hit to Short, the left fielder should be behind her, if there is a play at third, the left fielder needs to run hard to back up third.  For the most part, the pitcher stays in her circle.  If she is ever caught outside of the circle and the other team takes advantage of that, it is her fault.  Because this age group have not perfected their throwing and catching skills, other coaches will take advantage of that. For example stealing 2nd all day long because the catcher cannot throw down well enough.  I do not believe in this sort of play because it is not teaching the girls the real way to play the game.  I hope this helps!

Answer
Hello again, I just responded to this question and I forgot to add something...  in softball being an outfielder is a hard job.  Every pitch they should be backing up a potential throw if there are runners on and they always have to be aware of the plays so they can be there to back up.  As a coach, I practice infield with all my players so even the outfielders can understand what goes on in the infield.