Childrens Fairy book with a red cover.

So I read this book when I was around 9? So around 2015. It had a red border vignette and the middle had a cottage with an old looking wooden gate I believe the main character ( a Girl) was also on the cover looking over the fence. It was a longer form picture book from memory.

The story was about a girl and her brother staying with I believe their Grandmother? The girl ventured out into the forest next to the house to find a stream and a rock circle, which she steps into and goes into the fairy realm? Or becomes a fairy. But her brother while with some friends kicks the rock circle and breaks the connection she had to the human world. While looking into the stream I think he sees her and he has to fix the portal, returning her to the human realm and they go back to the cottage where they live hand in hand.

I remember the girl having blonde/very light brown hair in a bob? And I believe a green long sleeve top and jeans.

Thats all I really remember and I cannot for the life of me find the book. I tried asking my mum/siblings but they seriously don’t remember this either. I know I had dreams about a similar story line because of reading it. Or maybe I just dreamed it? Idk but I’m hoping for some help!