Not music to my ears

Well, this is the week I make Kiera cry it out at night. I have been getting up almost every night for 7 months and it has taken a toll. Last night she cried for about 30 minutes and I gave in because Kaitlyn started to get upset. I figured whats the point of two unhappy kids at 3am.
Right now it's 1:35am and she just gave up. She fell asleep at 11 and woke up at 12:25 so she cried for right at an hour. It just kills me to sit and listen to her cry, I know what she wants. Is this the right thing to do? Poor baby.
Maybe she's not as stubborn as her sister after all. We tried this with Kaitlyn back in the day and she screamed for three hours and when she threw up all over herself at that point I threw in the towel. To this day she rarely sleeps through the night. I am determined that Kiera will become a good sleeper once again. She was from two months old to seven months old. She is very smart, so hopefully she'll figure this out in a few short nights. Maybe even before James gets back from his trip. Lucky him getting to sleep in a quiet place.