Help finding a book

[PaintingPicture]

This has bugged me for years, a book I read around 2003 as a teen…

Main character was called Matilda but everyone called her Mattie, she went to high school and it was English. She went away in the summer holidays with her Dad (I think?!) and one of her parents met a new partner and they also had a Matilda who went by Tilly. I think she had a younger brother.

I read this book multiple times and cannot find it, Chat GPT has no idea either.

thank you!

This is ringing a bell with me but I don't know the title either.
I am having a good Google to see if I can figure it out because it will annoy my brain 🙂

Not rent a bridesmaid is it!?

@twigsand I think that might be where I am thinking of characters called Matty and Tilly but it's too new for the OP.
@PaintingPicture sorry.....I turned out to be no help 🙁

Oh thank you for even trying!