She made her choice for her life, now it's time to make the choice for yours. She can visit your kids often still, and if she wants to be around more kids, she can adopt, or be a foster parent, to volunteer in the big brother / big sister program.
Sometimes, you have to move your family for what is best for everyone... not just for one person.
We recently moved 7 hours away form all of our family and friends. My mom is a widow and lonely, but she has people there, though gave us a major guilt trip about moving. Well, we had to do what was best for us by taking the job.
She can always move to where you are, or who knows, in 10 years you guys might all move somewhere else together. Do not feel bad. You left all of your friends and family one time to be near her, now it's time for you to go and have a wonderful time, have more time with your husband, and save plenty of money for your kids' colleges and your retirement! You may be taking your daughter out of a school and community she loves, but possibly be putting her in one in which she will love more.
Oh, and 5 hours away, you guys can visit each other on the weekends and holidays! There was a time in the past, when people moved across the country or to a new country, they could never see each other again... but those days are over. You guys can email, text, send pics, and skype between visits.