a fellow umpire had this sit
 

League rules. . .First pitcher can pitch a max of 3 innings. . .The first pitcher may reenter to pitch only once (basically, she can pitch inning 1, 2 and then come back for the 6th or any derivation like that). Any part of an inning is considered a full inning under this rule. Any subsequent pitcher can pitch a max of three innings but is not allowed to reenter.

So here's how it was explained to me. Farm game 3rd and 4th graders

Pitcher completes inning #1, she comes out for inning #2. She is standing on the pitchers plate (having not thrown a warmup) when she is hit in the head by an errant ball. She is taken off the field. Pitcher #2 comes in to warm up. . .after throwing warmups, the #1 pitcher comes back from the bench. A discussion ensues on the validity for both pitchers.

I have never seen this before and the coaches decide "let it go" because its REC LEAGUE. I HATE "MEETING OF THE MINDS"

Assuming ASA - Strictly speaking isnt the following correct?. .
#1 pitcher re-enters (thats ok due to league rules)
#2 pitcher cannot come back into the game as a pitcher - (taking the mound even for warmups makes you a pitcher - right?). . .
#1 pitcher can still pitch into the 3rd inning.

Strictly ASA - No league rules here

A player may enter the pitcher position as often as possible as long as s/he wasn't removed by rule
Anyone can take the warm-ups and it does NOT make them the pitcher.
Pitcher can throw as long as the coach allows it.

Well ... when you're dealing with league rules that differ from the ruleset you're using, you often have to have meetings of the minds, in that in many cases the league rule is not written well and doesn't cover everything.

In this case, using ASA and the rule you gave, all I have here is pitcher #1 pitching her 2nd inning. The player you're referring to as #2 pitcher has not yet pitched.

Taking the mound for warmups doesn't make you a pitcher unless you're in Little League Baseball.