My guess is that Ron somehow knew that Cathy was going to be there (most logical being just following her) and simply took the picture with his phone by staying at the corner.
I was also thinking some more about Bella's room being a storage room for painful memories. It's a hunch and maybe a stretch, but I've got a feeling that you're theory about Miranda, Vivian (and Bella) didn't know about Tremolo's birth and/or Lynette's death. I think this for at least the following reason:
When talking about Maya, Tremolo mentions that while growing up, Neil did great on every day that mattered. Neil doesn't seem to agree:
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I don't think he only thinks about the day Lynette died, since imo that was before MC growing up. There must have been at least 1 moment later on that Neil thinks he made a bad decision for the wellbeing of MC. Maybe a fallout with MC's friends or simply leaving town without telling them about it? If so, there might be a picture in Bella's room with Neil, Baby Tremolo and 1 or more girls (most logical being at least Miranda, since she seems to have had a closer relationship with Miranda than Vivian).
There is a counterargument to this during the same meet, and that's that Neil only reacts happily with "That's a beautiful name" when MC mentions her name is Isabella. You would think there should pop up at least a thought if she also knew Lynette in the past, even if Neil wouldn't think of it being the same Bella (and to be honest, why would he?). This can simply be explained however by him not being as close to Bella as Lynette, Miranda and/or Vivian.