lo pal. it all depends i'm afraid.
just because the seeds are fems doesn't mean a bigger yield.
how many bulbs are you using?
what nutrients are using?
are you checking your ph and ppm/ec?
how long did you veg for?
i didn't say you overwater. as you say your others are doing good but that one pot may be to tightly packed but it looks like a classic sign of to much water in the soil.
when you say you didn't see anything i presume you mean you saw a nice greenish stem.
i wouldn't start tearing up roots...
if you need to stop the pump working, the easiest thing to do would be unplug the aerogarden and just run a power cord to the lights on a timer. you shouldn't do this tho until you get a decent root system going. feel free to post questions in my latest journal. all the best.
i would has at guess that it's to much water. wobbly stem is probably due to rot. if you move some of your soil away from the stem, what does it look like?