I thought it was more that she is feeling awkward because she's not sure what is appropriate or how to act towards her. You could see that she wanted to hug her when she first saw she was back and spill out all of her relationship troubles to her old friend, but held back because she suddenly realised, no, that's probably not appropriate any more.
It must be a bit of a weird situation - I can't think of a parallel really. Possibly like when you're a teenager, and your opposite sex friend gets a girlfriend, and you suddenly don't know whether you're allowed to hug him or have cosy chats any more. And nobody asks outright because it's the 1950s and it's not the done thing. I think they'll string it out for a few episodes and then they'll have a heart to heart where she says "I'm still the same person, you know".
I think Trixie is trying to be respectful and Cynthia is feeling a bit out of place, but neither of them feel able to say anything yet.