DinaFem auto Amnesia

This was a free bean I got, It popped very quick, started growing great and looked to be a very healthy lil girl. I thought I was onto a winner.

but a couple of weeks in and she seems to have stoped growing she still looks nice and green and healthy. I have changed nothing in that time.

This is a pic from a couple of days ago, she has hardly progressed at all.

Any ideas??

I'm using a 400w hps @ 20/4, she's in coco/perlite/vermiculite mix. I just gave her the first feed of dutch master nutes at a very week soloution.

The thing that has me stumped is she still looks healthy, no sings of anything. I have three other plants under the exact same conditions and they are fine.