This is certainly sad for both of you.
I was a male TA (now retired) in an infant school for ten years, and because I had not enjoyed school myself as a child, I tried to ensure the more vulnerable children I worked with received all the sympathetic support they needed. The TA is in a privileged position, as they can nurture children more personally than the teacher can, who is usually too busy with teaching, planning, meetings etc. to notice the emotional state of each child.
Do you know if there is a TA, or even 'parent helper', in the class who could 'look out' for DD when she is feeling low? Is she coping academically with subjects, and also getting involved with PE, games, drama, music, art & crafts, etc? It is difficult to make a full effort in things, when you are feeling worried, so her emotional state could start to impact on her progress. However, if there are any areas where she achieves really well, try and praise and encourage these, or might she benefit from attending club activities.
Does she have any special friends, or know any children in the older year groups, who she could talk to? At some stage there should be parents' meetings, so try and attend them, and raise your concerns, though it is possible the teacher in question might not be at it.