It really depends on if the baby in question likes it and is used to being in it. I have 4 kids. My boys loved the carrier--we used the Nojo baby sling (not sure if that's still available) from birth. By about a year, though, both boys were outgrowing riding in it, and just used it as their "love object". We took our youngest to WDW when he was 6mo, and the sling was a life-saver--he could peek out at the world, but then when he needed a break, we could just pull it up a little to give him a little cocoon.
OTOH, my girls hated that thing (and any other type of carrier). By 6 weeks old, my younger DD simply refused to be in it. My kids go girl-boy-girl-boy, so I didn't do anything different with the middle girl. She just didn't like it!
If your DD has a carrier, I suggest she try the baby in it, well before the trip. If it's something the baby is comfortable in, by all means, bring it. But if it doesn't work out for your DD, for whatever reason, then you know, and don't need to fret. I think you'd be okay with just a stroller, too--my kids weren't big on strollers, I have to say my sons, at least, logged way more hours in the sling than a stroller. My girls preferred to walk! They were very much "me do it" kids.