She stocks one roll in each of the 6 bathrooms, every day of the week so that 6*7 = <<6*7=42>>42 rolls a week
She restocks 42 rolls a week so after 4 weeks that's 42*4 = <<42*4=168>>168 rolls
The bulk toilet paper comes 1 dozen rolls in a pack and she needs 168 rolls so she needs 168/12 = <<168/12=14>>14 dozen
#### 14