Why would you send your child to a non-Catholic religious school where they will learn non-Catholic ideas?
A Catholic preschool will teach them Catholic prayers, the sign of the Cross, perhaps Mass attendance, the liturgical seasons, Saints, etc.
A non-Catholic, Christian preschool will teach non-Catholic forms of prayers and will not do the sign of the cross. They may even actively discourage the sign of the cross or tell your child it’s wrong were your child to try to begin his/her prayers that way. They won’t celebrate the seasons of the year, Saints, etc. Your child may even learn, subtly or outright, that things she believes in are “wrong.”
Children are inquisitive. If she asks at school “where are the statues?” or “why don’t you have a priest” or “can we pray the Hail Mary?” or “why don’t you do the sign of the cross?” well… you’ll have a problem. And, you’ll confuse your child.
Start your child out in the way he/she you want them to go. If you want to instill Catholic values and beliefs, send your child to a Catholic school.