Does her school not offer any training in this area?
I used to work in special school with students like her, and we had a number of projects in place. One was a week, sometimes two, during the school year where we took three or four students at a time, under the supervision of a couple of staff, to a flat where they had to work together cooking, cleaning, planning budgets, transport and activities with minimal input from staff. All this with appropriate classroom preparation, of course.
Is it possible your charge could perhaps plan and cook a simple meal each week, doing the budgeting and shopping and then the two of you (or an invited 'guest') could sit down and eat lunch together?
One of my remits at the school was transport. Depending on the ability of the student, we'd make an accompanied bus journey. Sometimes it would be the home/school journey. Practising this during the day, it would give student and myself a chance to chat with parents, if they were home, and get their input too. I'd gradually get the student to take more and more of the decisions about which bus to catch, where to get on and off etc., until I felt they were ready to do it alone. We'd give it a try, having a car ready for emergencies, and if that worked then they could get a council bus pass and come to school on their own.
If they had other stuff, such as short college courses or work experience, then we'd practice the journeys for those too. Sometimes they could do them in small groups, if they lived or were 'working' in the same area, and could support each other.