I think you'll be more comfortable with her next to you. On the rides with lap-bars (like Pooh, Peter Pan), I always put my toddler next to me and put my arm around him. On rides like Pirates, I might have let him sit on my lap so he could see better. I'm sure that the CMs will let you know if she needs to sit next to you due to the safety restraints.
It likely depends on the ride. I know at DLR, on many rides a young toddler or infant may sit in your lap but on at least a few they have to sit on the seat (so even though there is no height/age restriction, the baby must be able to sit up). I prefer my toddler in my lap because a) he can see better and b) then my 5yo can sit next to me as well (otherwise they fight over who gets to sit next to Mommy, and of course kids have to go on the inside, so Mommy' can't be in the middle).
I think you'll be more comfortable with her next to you. On the rides with lap-bars (like Pooh, Peter Pan), I always put my toddler next to me and put my arm around him. On rides like Pirates, I might have let him sit on my lap so he could see better. I'm sure that the CMs will let you know if she needs to sit next to you due to the safety restraints.