Example 1
Charlie's mom hyperventilated when she saw a speck of dust in the air, and then she asked him to clean the entire house.
After Charlie's mom caught her breath, she proceeded to assign him chores. Since an element of time is involved here, then is the correct word for this sentence.
Example 2
Michelle has more sparkly dresses than she could ever possibly wear, but she can't stop herself from buying a new one every time she goes shopping.
Michelle sounds like a princess. A princess with insane credit card bills. Here, than is the right word because two things are being compared: sparkly dresses owned and sparkly dresses that actually get worn.
Example 3
You would never know that I am taller than my sister because she always wears high heels.
Sounds like the speaker's sister is a wee bit insecure about her height. In this sentence, than is the correct word because it involves a comparison between two people's heights.