struggling with her desire for independence

[alita7]

My step daughter is 10 but due to brain damage due to a medical condition at birth (don't want to say in case it gives away who I am to people I know) and possible asd which she is currently being tested for, she is more like a 5 or 6 year old in almost every way except appearance. she came to live with us last year and she's generally very good and we get on really well.

The problem is in the past month or so she's started arguing more and her need for independence has grown. Unfortunately, she is unable to have this independence in most cases as she would either be in danger or it would take so much time shed be late for school etc. we try to encourage her to do things herself where possible but it's just not possible sometimes.
I think her arguing is also related, she is finding being told/asked what to do very difficult (especially when her sisters who are a bit older than her come to stay, as we don't have to tell them to clean their teeth, put on a coat etc, but we have to tell her, which makes her feel she is unfairly being told what to do). she has always been a child who needs why she needs to do something she doesn't want to do explained to her, but now she's starting to persistently argue against explanations. sometimes It's just awkward, like she wants to wear a certain coat when she needs to wear a waterproof one but sometimes it's seriously dangerous like when she decides shes fine walking on the edge of the pavement right next to a busy road... I'm finding it very difficult because it seems the only way to get her to do as she's told is to properly shout at her, even bribery or threatening to take away treats or privileges which used to work, no longer does. she doesn't do this with specific people it's me, her dad, grandparents... but it is a lot more common when she's with her sisters or if she's just seen her mum (which can upset her as she has very mixed emotions about her which she struggles to understand, due to the reason she came to us) but it isn't exclusively those times.
I don't think it's due to unhappiness as she seems fine most of the time particularly when she's doing what she does want to do. I just wish she'd want things that you can compromise on instead of to wear shorts in the winter or to not go to bed on time or to not do her homework or worse to cross the road even when she can see cars coming (I have on more than 1 occasion had her stubbornly try to pull me across main roads!) I think it's purely driven by her wanting the independence other people have and to make her own decisions.

any advice?

[alita7]

also forgot to mention that she seems to be starting early puberty, which the school also have mentioned. This might be having an impact. We noticed recently that just before I'm due on she gets very moody (though now I'm pregnant this may not happen) and I think her hormones might be syncing with mine.