I had two in diapers.....potty train that girl as soon as she'll let you!..haha

Um, what I found the most effective with my babies is to let them sort of hang around already potty trained children. My little boy went to Head start, and a week later he was on the pot and never turned back. He really wanted to be like the other kids. Then my daughter saw his accomplishments and decided to do so herself. It was an awesome chain of events...I was so happy.

Children really influence each other. If you have some young nieces/nephews, or friends with toddlers, or anybody like that...set up some play dates and leave the bathroom door open. An 18 month old will be curious and keep on eye on what's going on, she'll notice.

Good luck!