The 6-hour stretch may well continue, the main thing is to look at the baby's crying as communication, it's not them being difficult or doing it to frustrate you, but like a person speaking in a different language trying to get a message across. All your baby can do is cry, to say "I'm tired, I'm hungry, I'm bored, I'm upset" etc...
If she doesn't settle in the normal way & gets more upset it could be many things - bit of a tummy ache from too much of something you ate, or over stimulation, or bit of a cold developing etc... sometimes they just need that extra cuddle or that extra feed & it won't stop them from growing into a healthy responsible adult... it may mean you have a child who learns that when it asks for comfort it is given (which is actually a very good thing) rather than giving up asking because it got ignored too many times... That doesn't mean you have to be at the baby's side all the time, more that, if in doubt give love & attention (it's not true that you can spoil them by holding too much) rather than if in doubt leave them to cry.
I honestly (with the value of hindsight) think the worst thing any new mother can be told is "don't let them get into bad habits" Most of us forget so very much about what it really is like in the first year. One of the men I work with had his 3rd child last month & he said, it all came flooding back to me how unpredictable they are in the first few months" & I actually responded with "It keeps being unpredictable even when they are teenagers & you still need to "read between the lines"