Quick baptism = possible but not probable. Baptism in that era was typically done a few days after birth, IN CASE the child died. It is possible that Margaret may have been sickly but it is not an automatic conclusion. The infant mortality rate was very high and people didnt take chances, especially if they belonged to a church that believed in the idea of "original sin". (This belief of a quick baptism persists to this day - may dad was horrified that we waited six months to baptise our children.)
Margaret was most definately born at home. Hospital births are very much a 20th century practice. The baptism record you have is all you will find for her birth record and you are lucky to have it. There are many surviving records from the mid-1800s but many more have been lost over time...as you search for records, keep in mind these key points: a record had to have been made and it had to survive. If either of those 2 things didn't happen, you are out of luck. And as for the baptism being the only record, it is helpful to know that births at this time were not registered with the state or city (again, this is a 20th century practice in the US, at least on a widespread basis).
Hope this provides some clarification.
Lynn