I can understand how the sign poses a dilemma for you. I would consider disregarding the do-not-disturb sign one time. You could just say that you are very concerned, as it seems you are. Or . . . you could leave a note taped to her door, and see if the note gets taken in. Another option is to call local police and express your concern. They will visit her and simply inquire if she is all right. I'm not sure if they will conceal your identity as the person who called them. You could ask. She is likely to figure out who called anyway.

This was done for me once. I was okay. The police were very nice and not overly intrusive.