Not worth worrying about. Just sign it regardless of how long she spent on the homework. Middle kid took Spanish and French through AP level and I almost never saw her doing Spanish or French homework. I asked and she told me it was easy and she typically did the homework during a bit of free time during the school day. As long as your daughter is doing well in the class, I wouldn't monitor homework - just sign.
As for 45 minutes of homework, that was the standard at my school. Five core subjects, had four of the five each school day, so 45 minutes times 4 subjects each night - three hours a night. Sometimes it wasn't quite that much, sometimes a bit more, but you manage. And then when the college freshmen are complaining that they have so much more work than in HS, you are relieved that you have less work in college.
