((*Will mark brainiest to the first right answer for my question AND my riddle ;>*)) Which of the following statements is true?

Before Jenner's vaccine, there was no prevention for smallpox.
Edward Jenner developed the first vaccine for cowpox.
Vaccination is only necessary for children under 5 years old.
Missed vaccinations can be given during "catch-up" periods.

*Riddle Time!*

A girl, at the funeral of her mother, met a guy whom she did not know. The girl fell for the guy and wanted to contact him. She looks for him but couldn’t find him. A few days later she kills her sister. Why did she do that?