My question is. My daugther is 19 years old, a full time student and lives at home. Now if she gets married before she turns 21 will she still be able to receive child support?

No if she becomes married then she is considered emancipated.

There are several ways that she can become emancipated ( in terms of child support)

And of course why should it continue, child support is to pay for her expense for your cost at home for raising the child. When she is married that is her and her husbands duty.

Easy question. Easy answer, no. The child support is not for the child it is to help the custodial parent out with the cost of raising a child. By getting married she is obviously saying that she is an adult and child support stops.