As far as I can read, your DD says not today and the boy then leaves her alone for the day and asks then the next day?
The boy has never made any romantic advances at all and all the talk for BF/GF is rumours?
Your DD likes him as a friend and doesn’t want more but wants to keep him as a friend maybe walking the dog a couple of times a week?
The poor boy doesn’t seem evil to me, according to MN I think no male can ever ask out a female or they are an entitled abuser. He is 16.
My suggestion if your DD wants to or needs to nip it in the bud would be honesty, firstly if I was your DD I would talk to him when out on a walk, just say how annoying it is that people think they are a couple when they are not and will never be. Make sure he understands he is in the ‘friend zone’ and if she values him as a friend to tell him that too. Next I would say that I like to walk the dog alone sometimes and arrange to meet 1 or 2 times a week. Again only if she wants to.
The other thing she can do, if the boys friendship and company isn’t important to her, which again is valid at 16 is to just say it’s been nice walking with him but that she wants to walk the dogs alone as it’s good for clearing her head and getting some time alone. Again I would say this only if true.
I suppose then if the boy keeps trying he doesn’t understand and should be told in no uncertain terms she isn’t interested and won’t be walking with him anymore.
I don’t think it will come to that though either he really is just a friend or he has a silent crush and will get over it.
Boys are not all evil.