I have had some similar issues with my now 5 year old who has a form of high-functioning autism ( I have a baby and an 8 year old, too) For now, we rarely take the 5 year old to Mass. The sound, being in a room with lots of people, etc, is too much for him. My husband and I attend separate Masses so one of us can be home with DS.
I don’t know what state you are in, but in most states, children with behavioral/mental health issues are elgible for early interventon services. If she isn’t getting them. call your local Intermediate Unit or the special education dept in your local school district. Either will be able to give you the right people to contact. There is respite care available for parents of special needs children.( hav an exceptional child means having to advocate for them often to get them the services they need to live a full life. I would look into getting bhavioral support ASAP. I have learned a lot from his therapists. They will teach you skills to help you help your daughter. Early Intervention is available to all qualified children no matter the family income. These services are unrelated to anything she qualifies as a “military” child. With respite care, a trained therapist would watch your child while you go to mass, run errands or do activities with your other child.
I’m sure there is another family in your parish with a special needs child. Most parishes offer several Masses over the weekend. Perhaps you could attend Mass with your baby and then switch off with the other family.
I would also talk to your parish about your desire to join the church. Some parishes allow candidates ( people who have been baptised, but not confirmed in the Church) to recieve religious instruction one-on-one. Of course I’m not making promises, but I have a good feeling that they will “work with you.”
God Bless you and your family. I am grateful for your husband’s service to our country.