I have been to many many protests where the venue is far away from a public area like a sidewalk. If Sylvia will be at place with a main entrance to enter a parking area, that would be a good spot. Only a bad spot when there are several entrances and not enough people. People would see you and your signs and would have to drive past. Little chance to hand out fliers but short, to-the-point signs will be remembered.
http://www.lakewoodtheater.com/booking
And a map
(this is just basic info. I don't know this particular venue, and you would know the area better than I)
If anyone can drop by when a different show is going on there, they can see where the traffic goes and get ideas on the best place to be.
As far as putting it online...it is not an intimation thing. Sylvia Browne is nothing to me as well being nothing to you. Anything her people would do you will end up online and just make her look worse.
You just have to decide how much warning you want to give her. Scientology is much worse. When scientology knows they will be protested, they have taken out film permits or city sidewalk permits for the same day, and then blocking people from normally open sidewalks. They also hire off duty LAPD to act as security. But this costs money, so you are probably safe from stuff like that. And there may be security guards there. They will tell you to move away, you can't stand on the sidewalk, blah blah blah. Unless you are blocking the sidewalk, it is not an issue. That is their job so don't believe them. They will not be on your side. Sylvia is generating money for them and you are not. Wait for a cop. Letting the local police know ahead of time is also helpful. They can confirm law relating to signs. In L.A., the only real issue is the length and thickness of poles for signs (if you use poles) so they cannot be used as weapons. If you are not causing a disturbance, using amplified sound, etc...the worst they can say is that you can't stand in one place and must walk. But that just means more people will see your signs. If police do come, have video cameras ready to gets faces and badge numbers in case there is any issue. I really doubt it for something like Sylvia Browne, though.
So you just have to decide if you want to give her a lot of warning. The positive is that you are making her have to worry about it and work on stage knowing she will be confronted. Hell...state you will be there even if you are not. Making her paranoid is also fun. But I can also see being quiet about the protest until the day of, so she gets a nice surprise.