S.,
Nursing at this age is fine, as long as BOTH parties involved want to continue. If you are content to keep nursing, and she still wants to, then it's really none of anyone's business. Tell them she stopped if it makes you feel better. What you do in your own home in the middle of the night is your own, you know?
Now, if the time comes that you are ready to stop, my best suggestion is don't offer, don't refuse. If she asks to nurse, fine, but don't sit her down to do it, and don't tell her no. If you want to hedge your bets, offer her a sippy cup of warm milk, and a little snack before the time she'd be ready to nurse. For my son, it's Ovaltine warm before bed, but there's sugar in that, and not everyones okay with that. I also give him a few graham crackers or cookies, but again, what you give is up to you. She may be less likely to ask to nurse with an already full belly. Also, it may be the closeness and attention that she enjoys about nursing. So, snuggle her up with her milk, read her a story or sing asong, so she feels close to you and comforted. Try to make the experience as much like nursing as possible, without the breast. This works for some kids, but others associate the snuggle time with nursing, and it strengthens the desire, so you may have to go with trial and error. Some kidsreally won't learn to sleep without nrusing when Mom's around, like one of the PP's said. Then you might want to take an evening walk, or run an errand at bedtime.
Again, this is for you IF you're ready to wean. If not, nurse on, Mama!