In her 3rd vegetation week, I finally started actually watering her. I still sprayed the surface, more generously now, to prepare the soil to take up all the water. She got 2x500ml (on two days in a row), the first 500ml with some Bio-Grow (2ml/liter). As this is my very first grow, I was very careful with giving any nutrients, as I did not know whether the soil nutrients were already enough. She seemed to like what I did, though.
Having the fans in the tent running (I keep them running 24/7) also seemed to help a lot with the stem. It thickened each day and became stronger. This was especially important because of how much she stretched in her first week