Thanks for the suggestions guys. A couple of things:

When DD was around 3 months she was sleeping about 10-12 hrs in a row so she does have the ability to do it!!

I thought maybe she was having too many sleeps during day and could stay awake longer but to be honest, if she's awake for much longer than 2 hrs (sometimes 2 1/2) then she gets cranky. If I miss putting her down, even by 15 mins then she becomes overtired. She rarely cries or gets cranky if I get her down in time IYKWIM.

Can babies who don't have a routine when babies have one when they are toddlers successfully?