I am apparently denying them of their RIGHT to see their newborn grandchild/niece.
I had exactly the same problem. DP's brother was in a big accident a few months ago and while we all went down to see him at the hospital he got quite annoyed that everyone was there. My DP thought this was an opportune time to bring up the fact that I didnt was visitors while I was in hospital. The convo went a little like this:

DP: You know Danni is the same she doesn't want any visitors when she gives birth
Aunt in law: No of course we aren't going to be in there while she is giving birth. We will wait in the waiting room.
(me slightly freaked out now and getting quite annoyed that this had even been bought up)
Me: Um no, actually I don't want anyone visiting until we get home, I just want some..... (I get cut off)
Aunt in Law: We have rights you know, especially FIL, you can't deny him the right to see his grandchild.
Me: Yeah

I left it after that - no point in arguing with them - I took it up with DP after we left. In fact I threatened DP that he had crossed the line bringing it up and not standing up for me and I wasn't even going to tell him when I went into labour!!! Apparently now he has come around and decided not to tell them until at least a few hours after the birth but I have enlisted my best friend as a support person (which I think has annoyed him a little) so she can keep him in line too!!!

We are lucky in that the hospital is moving and no one is going to know whih hospital we will be in - we wont even know until that day so in order for anyone to just show up they have to make possibly two trips.

I don't at all think you are out of line I think you are being reasonable. People don't seem to realise that yes their niece/nephew, grandchild, random work friends baby (lol - she being the most out of line)WHOEVER is being born but it is US MUMS who have to go through labour and birth and it is hard work and sometimes traumatic or overwhelming and WE created this little baby and i think that WE should have the RIGHT to spend some time alone with him/her.

People like this make me so angry!!!! I can't think of anything worse then people waiting for the impending birth either.

I also don't really think it should be up to you to say something to this work collegue. It might be easier on Shell if you do because she has to work with her but I think it would be nice if she just maybe said to her that you didn't know her that well yet and didn't really feel comfortable with calling her granny and maybe offer for her to meet up for dinner more often or something so you can get to know her better. I dunno - I'm talking mish mash.

Point is - Stand up and be heard - DO NOT GET PUSHED AROUND!!! This isnt about anyone other then you Shell and the bubs - remember that!!