maybe just write a note being honest, say you noticed and didnt know what to say at the time, but that you are concerned for her, and hope she is ok - add your number and say if she wants to talk etc that you are there.
not sure about turning up with gifts - she is practically a stranger so it may seem odd just to knock, and you are also putting her on the spot to invite you in, there and then, and explain etc, when she probably wont want to - but do add in the note that you will come round for a cuppa if she wants and will bring a jar of homemade jam! - then if she wants to talk she will message you.
i mean we all have tough times, we all cry etc - doesn't mean we need or want people we don't know asking etc.