Number problem of the subject

The passage below is from “Don't Sweat the Small Stuff for Teens.”
In the underlined part of it, the author perhaps used ‘were’ because Kelly suffered two horrible events in one day. But in a grammatical sense the verb ‘were’ seems odd to me. In the sense that the subject is ‘that clause’ and that we consider a clause the singular, the verb should be ‘was.’

What do you think of my line of thinking?

Thanks in advance.

http://books.google.co.kr/books?id=WJ8L5jeGZ1AC&pg=PA49&lpg=PA49&dq=%22Kelly+said+that+when+she+was+eighteen+years+old%22&source=bl&ots=PeHRHcs1AW&sig=Pu2mR14KF_PhjZuwFx3sTTHT23w&hl=en&sa=X&ei=SiDdUv-0LsjniAephoCQDQ&ved=0CCUQ6AEwAA#v=onepage&q=%22Kelly%20said%20that%20when%20she%20was%20eighteen%20years%20old%22&f=false

Kelly said that when she was eighteen years old, she had what she believed was the "worst day of her life." Among the horrible things she experienced that day were that her mom's car was hit in the school parking lot, and her backpack, which contained the only copy of her research paper, was stolen. She said that her desire to not sweat the small stuff, along with her acceptance of the fact that everyone has an occasional horrible day, saved her sanity.