Honestly, as I learnt not to stress the small stuff, I'd throw the 'it might become a bad habit' out the window and provide your DD with the comfort she is seeking. As you have a cold, chances are she could have a sore throat and she's telling you what works. Babies and children never do things that aren't motivated by a real need (even if we can't see it) so I'd follow her lead.
From the Mum of teens (and step Grandma) honestly this time is but a blip in their lives and babies who are poor sleepers can become amazing 16yos... You won't raise a 'problem' child by following their lead infact you'll probably raise a good one.
