What?
It's 5 sent per hour (assuming 8 hours of sleep).
That's one every 12 minutes. Where the heck does 1 every 3 minutes come from?
If she was sending 1 every 3 minutes, the monthly tally would be roughly 19,000 messages!
Hardly the case here.
First, do me the favor of reading the post I referencing, then I will spell this out for you...
5 texts/hour * 24 hours/day * 30 days/month = 3,600 text messages (so clearly this is a lower estimate than the actual usage)
Now, obviously you can not text continally 24 hours per day, so I assume there are about 12 hours per day where texting is acceptable, accounting for sleep and the majority of time in school where texting is prohibited. To estimate texts/hour now we have:
3,600 texts/month / 30 days/month / 12 hours/day = 10 texts/hour.
1/10 hour/text * 60 min/hour = 6 min/text.
So she sends a text message every 6 minutes on average. Usually you receive a text message in response (so double the number of texts) and you get 1 text message every 3 mintues. That is either a message she is reading or one she is writing - both requiring diverted time and attention otherwise spent on babysitting.