My DSD just turned 7. She picks out her own clothes for both school and weekends, takes her plate through after tea and scrapes remains into the green caddy, can either load her plate into the dishwasher or leave it at the sink (depends whether DW is full), sets the table, makes her bed, puts toys away, uses a knife and fork, washes/conditions her own hair and dries herself off and gets dressed after a bath or swimming lessons.
However, a lot of this is still with guidance. There are sometimes strong recommendations for clothes, depending on weather/activity. If her plate is loaded with leftovers and she's having a hard time carrying, we might take it off her and finish the job. She still needs coaching through shampooing and conditioning her own hair, especially if she's in the shower after swimming lessons (gets distracted by other kids' chat). She needs to be reminded to actually use the fork and knife at the side of her plate and not talk with her mouth full.
I remember asking my DH "shouldn't she be doing that" a lot when I first met his daughter. I think that's just what happens when an "outsider" gets a really intimate look at a family. There was also some regressive behaviour ("I can't, you do it Daddeeee") when it became clear to DSD that I was moving in. It was likely attention-seeking, and seems to be normal by all accounts, even in bio families. E.g., a good friend of mine recently experienced this with her DD2 after her DD3 was born - suddenly DD2 didn't know how to put on socks.
It gets better, but you and your DH will both need to expect the same behaviour of your DSD for her to become more independent. Otherwise, she will just be able to play you two off each other. Any new task or responsibility, I've found, is best introduced on a weekend when everyone has more time to be patient, rather than first thing Monday morning. Picking out your own clothes is an easy one to start with - if she gets wound up about making the "right" choice, you or DH can narrow it down to two or three outfits and have her pick one for the day.