If we agree that we are dealing with the willful killing of defenseless, innocent life, then we can move to an apt analogy of the situation. If not, then I guess you would need to make the case that abortion is NOT the willful killing of defenseless, innocent life..
The analogy:
You watch a mother, with a knife to her young daughter's throat, go into a doctor's office. The doctor has told you previously that you are not welcome in his office. The young girl is in imminent danger, so you rush into the office to help save the young girl.
Later, after rescuing the girl, you take her to your church to get her some counseling and start the process of getting her to a good home...and her mother comes into the church foyer, with the knife, looking for her daughter.
Obviously, we are morally obliged to protect the daughter in both cases, and such obligation supersedes our moral obligation to respect the wishes of the doctor (even if he is OK with, or intends to help, the mother killing her daughter in his office). An abortionist is SEEKING innocent babies to kill when he/she promotes his/her services.
As someone else has pointed out, the pro-lifer in abortion clinic/atheist in church is really not a analogy - but the pro-lifer in abortion clinic/abortionist in church is. That is why I have the mother coming into the church looking for her daughter. (As also stated, the atheist would likely be invited into a discussion of his/her beliefs.)
So, on the face of it, none of us have the right to go onto private property where we are not welcome - UNLESS a greater moral imperative demands we do so. It is easier to see this when the law is morally correct, as it is in the case of the mother ready to kill her young daughter. Any accusation of trespass by the doctor would be laughed out of court. It is more difficult to see when the law allows, even supports, an immoral act, as the law does abortion.
Also - think of this: At a certain point in our history, men “owned” slaves. The law said it was illegal to assist a slave (the “property” of another man) to escape. It was also illegal to “help” another man's horse “escape” the barn. Would one have been a hypocrite in those days to assist a slave in his escape and demand prosecution of a horsethief?
That’s at least a more reasoned argument than I’ve gotten from most on here. The ‘greater moral imperative’ idea was the foundation of the operation rescue (Now Operation Save America) but I’ve never been entirely comfortable with it. I don’t see any New Testament example of Jesus or the early disciples insinuating themselves into the pagan practices of the day (including child sacrifice) in order to save a life or bring about some greater moral good.
Your example of assisting run away slaves (or helping Jews during Nazi oppression) holds some water but I’m not aware of anyone going to a slave owners property and physically trying to free them. And by the way I would have no problem with this woman doing her ministry on a public sidewalk.
In the final analysis I suppose if she truly feels she is called of God to do this she should rejoice in being counted worthy to suffer persecution and prison for her Lord.