Step daughter with ADD

[Gen45]

I am struggling to cope with my step daughter, she is 17 and acts like 9, she isn't maturing and I've known her two years and lived with her 8 months, my kids aged 12 and 14 are struggling too, I feel terrible that I can't gel with her and what I've put my kids through,
Anyone else in this situation? I need help please

OP have you looked in the SN section? There will be lots of posters who have personal experience of caring for teenagers with ADD in there.

SN section? What's that? I'm new to mumsnet!

The are talk topics of SN Chat and SN Children that are popular. You have to look for them as they don't appear on a Active threads unless you've opted in to them.

Our DS has ADHD, children can be developmentally younger and their behaviours can come across as less mature, it might just have to be something you have to get used to.

Can you look up to see if there is a local group for siblings of children with SENs, SIBS is the national charity... www.sibs.org.uk/

And might be worth seeing if you could attend a parenting course (though they tend to be few and far between). The Additude website is also a mine of information and advice too.