Hi Greenstuff87
Yes from what can be seen from the pictures it looks like overwatering which has caused nutrition lockout.
Over watering is the roots for many other problems to start.
You done first step by cutting the water.
If fully dry water her around 1-2 cm from steam With no more then 100ml daily. Or Even every second day for now.
Try mixing the soil gently around the seedling so you have better air movement around roots. If feels to compressed.
Hopefully she will get over it and start making new leaves soon. Humidity I keep around 50%. So should be good.
When she starts getting up nutrition up again and starts spreading her root system. She will start production of next leaves.
Hopefully this help and hope she recovers.
Good luck growing.
