Hi Vally
My DS feeds more often when sick. He still does at 16 months. I think its still such early days for you. 3 weeks is still so brand new and she has a cold. I don't think you can create a snacker at this age. My advice would be to go with the flow, feed when she needs to, let her recuperate from the birth experience and her cold (and you too!) also at this age i dont think you can jump in too soon, there is no real structure for another month or more.
Don't worry about bad habits just yet, there is time to work those things out, for the moment give her what she needs, do what feels right for you and hopefully get some rest yourself.
sending you massive hugs
xo