Taking stock, I empathise with you! It is an incredibly difficult time when 17/18 year olds are in that weird phase of being a 'semi-adult, so still working, looking grown up and acting like a kid (also read self-centred and entitled at times, but often just struggling to understand what being a grown up entails.. Ie scarey!)
Re you DD, if she is receptive then an honest conversation would help, so not just saying "shape up or ship out" but rather "Id like to talk about your living arrangements" and give her a few honest facts in a kind way. It would help to make it a two-way conversation so she has the chance to talk as well, hopefully she will want to do this. For example
- it is no longer a viable situation her drifting between households, you would like to "agree" (being the important word so she doesnt feel completely cut adrift from her home) the arrangement from now on.
- you recognise her growing maturity and want her to make the decisiin what to do, because it is her future. But at the same time, she needs to understand the impact on her family.
-as an adult you expect a minimum standard when she is at home and it is not acceptable to treat the place like a boarding house (tough love here) also some words about the disruption to routine, mealtimes, not knowing whether she is here, there, on Mars etc.
-that you love her of course! And that she always has a home with you, but you need the decision to be made rather than it just drifting along with no agreement being made between you both.
In a nutshell, positive affirmations, recognition of adulthood, but also a clear message that her current standards of cleanliness and general behaviour is not acceptable.
I am sure she will respect you for it (even if she doesn't like the immediacy of the situation and putting the decision to her, "wake up and smell the coffee" adulthood isnt a bed of roses type message)
Believe me, I have been rehearsing this one over and over, it will be visited upon me and DP in the near-ish future!