This is a children’s 7/8 age group
From mid 60’s
Paperback
Young girl enters over a wall of an abandoned house and ends up going back in time to carriage days and the family who lives there takes her in. Book ends with her returning back over the wall to home having not been gone long.
It might be The Wicked, Wicked Ladies in the Haunted House.
https://www.goodreads.com/book/show/1110801.The_Wicked_Wicked_Ladies_in_the_Haunted_House
Maureen is a mean girl in her neighborhood, and she’s fascinated by an empty old house that other people are afraid to go near. One day, she sneaks in there, sneers at the paintings of old-fashioned ladies in fancy clothes, and steals a bracelet that she finds. However, the fine but cruel ladies want their bracelet back. The house is haunted, but in kind of a confusing way, if I remember right. The ladies take Maureen back in time to when they were young girls living in the house. Their parents are kind people, and they take Maureen in and take care of her when it seems like she’s lost. In front of their parents, the girls always act nice in front of their parents, but behind their backs, they are cruel and shallow. Eventually, Maureen escapes back to her own time and is a changed person because she doesn’t want to be like the stupid, cruel, and shallow girls who haunt the house.
This was my favorite book as a child and is called The Wicked Pigeon Ladies in the Garden by Mary Chase. It was later reprinted with a different title, different illustrator, and some word changes. Here is a blog post that tells about both copies of this book. http://buildinglifelongreaders.blogspot.com/2015/09/throwback-thursday-wicked-pigeon-ladies.html?m=1
This could be Jean Slaughter Doty’s Can I Get There by Candlelight? A girl moves temporarily into a carriage house while a new house is building. She rides her pony through the gate of a stone fence into an estate where she meets a girl of own age. She gradually realizes the other girl isn’t delusional or playing dress-up but is back in time.
Is it Hunky-Dory Dairy by Anne Morrow Lindbergh?