Best books for teaching assertiveness/boundaries for kids

[Christmasalreadyinourhouse]

I'd love some recommendations for DD7 who is doormat with all her friends. She was bullied badly by one of them at school, luckily she's not in her life anymore.

She won't listen to me when I try to explain that it's ok to say no or not allow anyone to mistreat her. I despair!

I'm not sure if this is quite right, but you can get transactional analysis books that might help eg TA for Kids

Thank you. I looked on Amazon, there are loads of books on boundaries and TA but not sure how good they are. I'll search at the local library too. I ordered one on saying no, let's hope it helps a bit.