Toulouse welcome to the forum
I am sad you must come here for answers.
I do not have experience or knowledge regarding young children on anti depressant meds. Although I have been suicidal since 6yrs of age. I won't explain why at this time. Everyone is different, events and environments effect children on an individual basis. If the time comes, I think you would benefit from my experience I will tell you.
I will say, I am 59. When I was a kid, not one talked about
this, I was just sad, Snap out of it. Your daughter is getting help, good job!
The fact the therapist is doing daily therapy immediately is encouraging. The therapist seems to be well informed and concerned for your child. This is what you want.
There may be an even more trying time ahead for you, once the cause of the depression is discovered. Once therapists knows what the cause or partial cause is, healing can begin. It might also be a chemical unbalance in her brain.
This will be near impossible for you, however, try not to catastrophize. Learn mindfulness for children and yourself, use it it to stay in the moment, it will make your daughter feel more secure if you are calm around her.
suggest you find a support group! The second link has a link on the left side for Support Groups.
You and your wife are not alone in this, although you feel you are, this is normal. Ask the therapist
for references on books or materials that would help you manage your selves and your daughter, as you all journey thru this. All of you are going into the unknown and are scared. This does not make you weak, it a human and loving response.
Please keep posting we are here to support and validate, we do not judge. I ask you not to judge yourself somethings are out of parents control. I will stay with you as long as you post.
Here are some links that may help. https://www.verywellmind.com/youth-suicide-facts-1066787https://www.verywellmind.com/youth-suicide-facts-1066787