I’m going to guess she was very close to her father when the bomb went off. According to reports, a message (phone number?) was sent to all of the intercepted Hezbollah pagers at 3pm local time (IIRC), after a couple of seconds, the bomb went off. So a likely scenario is the father had the girl on his lap, the pager starts buzzing/ringing, dad reaches into his pocket and pulls out the pager to read the message. Proximity to the pager killed the girl while only injuring dad since he has a much greater body mass. Or, perhaps the pager was laying on a table and the girl picked it up? It’s sad, either way.
And Hezbollah doesn’t care about any civilians that get killed near them. ‘Involuntary Martyrs’ is the term I believe they used. According to reports, only 14 people have died, which is an extraordinarily low number considering that Israel went after thousands of targets that don’t wear uniforms and deliberately intermix freely amongst civilians.