Dishwasher Conundrum

so a friend of ours has a dishwasher that has not been draining properly and it started when she changed out the garbage disposal.

I know what your thinking, and yes, she knocked out the plug in the disposal.

We went over there Saturday to see if we could help out and this is very interesting.

Dishwasher drain lines goes to an airator and then down to the garbage disposal.  When it finished running there is still water left in the bottom of the washer.  I went through and checked all the fittings and made sure everything was tight and no blockage and stuf like that.

I removed the drain hose from the garbage disposal and put it straight down the drain (into the trap) and ran the dishwasher.  Everything ran fine, it emptied all the water no problem.  Put it all back like normal and it does not empty right.  I even watched it push water out through the drain, no issues.

only thought I had was the drain line was too long because it came off the airator and dipped down before it hit the disposal, so i cut some of it off and tried again, no dice, still doesn't drain.

I have been doing some research and cant find anything that would indicate what the issue is.

Very frustrating.

DD