At what point do you step back and let them fall?

My youngest (will be 17 in Dec) started her first day at her work placement today.  I ended up driving her to the bus stop with 2 minutes to spare and added yet more grey hairs to my extensive collection.

She really is the most unorganised, lacksydaisical person I know.  She was constantly late for school, loses things etc.  I'm forever chivvying after her reminding her of stuff. 
Yesterday I looked up bus times for her and told her the bus was at 8.20am.   This morning at 8am when I got back from walking the dog she was casually putting make up on in her dressing gown.   So I reminded her she only had 15 minutes till she had to leave for the bus and she said I told her the bus was at 8.30, obviously she wasn't listening to me yesterday.  Nothing new there.
Cue mad dash with much huffing and puffing on her part.

Really, we had a long talk in the holidays about how important it is to be on time for work and how she needs to be organised with all her stuff ready the night before and I thought she'd taken it on board but it seems not.
If she had to get herself up , make her own lunch and then make her way to work/school without me nagging she would end up late and hungry more often than not.   Which is a shocking thing to say about a girl her age.  I can't believe she still relies on me so much.

Is this the point I back off and let her deal with the consequences?  Deep down I think it is but I feel like  I should do everything I can to support her.  Maybe the molly coddling is doing more harm than good though?  I don't know, I'm just so confused!!

If it were me reading this from someone else I just know I'd be advising them to back off but it's so hard when it's your own.  
She is so immature compared to her sister at the same age ( I know you shouldn't compare but it's human nature I think..)

ursh x