Who should have this conversation with my step-daughter? (Details inside)

I am having a couple of (smallish) issues with my (22 year-old) step-daughter and her assistance around the house. She will do things like leave her dirty dishes in the sink rather than washing them, or cram more garbage in a full bag rather than taking the trash out. Like I said, smallish stuff, but stuff that makes more work for me. I have discussed this with my husband and we are not sure the best course of action. I have a good relationship with her and would like to keep it that way, so I am not super comfortable discussing this with her and looking like the wicked step-mother. DH had issues with his ex-wife trying to force him to do her bidding with his daughter, so he is gun shy about being put in the middle. My question is, what is the best way to address this with her? My best idea at this point is for DH and me to do it together, but that brings the potential for her to feel ganged up on. Thoughts?

If it makes any difference and just as an FYI, she lives with us with her two children age 5 and 3.