If she had stayed outside the gate and just asked her random questions and blah blah blah then whatever fine. But she came onto your property uninvited. that would have immediately warranted the "get off" response in my house. I'm a pretty trusting person but I have boundaries which apparently this lady didn't. I think you did the right thing. I wouldn't worry about her walking by a second time, she could just live that direction. but if she starts like loitering around then i'd get nervous.
Hope she stays away from you and your baby.