I don't disagree that the woman should have signed the ticket and gone her merry way, but to be tasered for a non violent act to an eight month pregnant woman - my guess is the officer wanted to see what it looked like to taser a pregnant woman (the officer was really, really stupid, and should be dismissed from the force).
I've never had a moving violation, but fail to understand why you have to sign the ticket. You either take it and pay the fine or go to court and contest it. What difference does it make if you sign it when it is issued? If you ignore it, they will issue a bench warrant so they are protected.
That said, I noticed that after they used the taser, 2 policemen forced her out of the car (one pushing), got her on the ground and handcuffed her.
I would never advocate breaking the law, but this sure seems like overkill in this situation.