Sleepless in Seattle (close enough) in Oregon ..zzzzzzzzzzzzzz??????????????

We have been trying to get our almost 3 and a half year old to sleep thru the night in her toddler bed without waking for a pee break, water break or shrieking her brakes ( the crying that goes on in the middle of the night does sound like that) for the last 6 months and it has not been working so far. We have tried keeping a light on in her room, even telling her that she will get a reward for doing that, even got to the point of scaring her but we haven't since we are still partly sane. We have talked to her pediatrician and she recommended the sticker system. But all has failed. With a new baby it is so hard to stick to the rules that you have made and that is what I think that these little nighttime visitors prey on. They know that my folks are so tired that at this point they will just give in to me. Whatever happened to that girl that we had trained to sleep through the night without one sound ????????? whatever happened to my angel who never complained about being scared ??? I dread every night that she will come and I dream that tonight she will sleep through the night. When I was ready to have my baby I thought it will be tough to wake up for the midnight feedings, but boy did I forget my older child. She is the one who wakes us up more than the baby. There are days when I think where did I go wrong ?? Tonight I go to bed with one thought and just one thought that maybe just maybe she won't show up...................