Situation:
Defensive player with possession of the ball and in legal position as offensive player begins slide. Defensive player loses possession of ball as she attempts tag on runner. The ball falls between the runner and the defensive player who scrambles for control and the tag. The ball is loose, on the ground, and along the base line between the runner and the base. Defensive player reaches for the ball as the runner slides. She grabs the ball and is met by the sliding runner, and tags her out, a foot before the base.
Anything here?

Depends... was the runner impeded by the defender while the defender did not have the ball?

Too right Dakota .
Always ask that question .
Just the act of being there is not obstruction and one step further even blocking the base isnt if there is no impedence of the runner .
So in this case the slide is on and from what I can gather only the body without the ball stopping the slide would constitute obstruction .

An umpire can never be too right! ;)

Of course they can you just need to look at the score book .
Everything the Ump does is recorded and as it appears in the score book it must be right .
LOL

Be careful here.
Follow the route of the ball from possession in legal position to the loss of possession to the completion of the play.

That depends on scenario but the definition of Obstruction is where a runner is IMPEDED .
No impedence no obstruction .
In this situation the slide is on and the only way we can have obstruction is if the defensive players foot, body stops contact with the base if they havnt got the ball .
Again blocking a base is not automatically obstruction , you only give a delayed dead ball when the runner is impeded .

There is no obstruction merely by being between the runner and the base without the ball. The runner must be impeded, meaning the runner did something that delayed or stopped her progress to the base due to the defender's actions when the defender did not have the ball.

If the defender regained possession of the ball and THEN blocked the runner, that is entirely legal. It is called making a tag.