D.B.
you have to remember that days, weeks and months don't add up according to general math. There's generally 30 days or 4 weeks in a month, but 7 (#days per week) x 4 (#weeks per month)= 28, not 30 or 31 as in some months. So we get a few extra days every month and after two months you are closer to having a whole week giving us nearly 9 weeks for every two months, not 8 like you would get with regular math. Its all because of those couple extra days each month that makes the math not quite "correct".
Basically you are right with both answers. It the same stupid math we all had trouble with when we were pregnant (40 weeks = 9 months, not 10!) Remember we have 52 weeks in a year but yet if you take 4 weeks and multiply it by 12 (#of months in a year) you get 48. Where's the missing 4 weeks? In those few extra days we get each month.
I started going by months after my kids turned 4 months. Most people don't want to put all the effort into figuring out what x weeks is in months anyways.
Hope that wasn't too confusing.
Congrats on for your daughter!