Alright, first of all, saying that they've had no chemistry so far, is completely false. Chemistry is not a term for solely love relationships; chemistry is especially important in the first meetings of two person, it describes if people simply "click" and if they understand each other without much need for words, if people simply feel the same. It's very complex. Shinichi and Ran share an enourmous chemistry.
Why would his work be disturbed by Ran? She is quite used to him solving cases; he really started to work with the police after their New York Trip, which was also the time she realized how much she loved him. Never did we see Ran having problems or getting angry with Shinichi for solving cases. Even as Shinichi made his trip alone to East Ohuko Village, we don't have any evidence that got overly worried or even angry at all. The reason, why Ran is so worried is, because Shinichi simply vanishes. The circumstances are not normal. If he could/would tell her where he is and what the case is about, than I doubt Ran would worry even close to as much as she's currently doing - which is not much by the way. Ever since London, Ran isn't really actively angry or worrying or crying for Shinichi anymore. Because she trusts him.
Also, don't forget that Ran has grown up with her family being at risk due to law enforcement/detective work. She grew up as a policemens daughter; I doubt she would go into a frenzy evertime Shinichi had case, especially since Conan and Kogoro regularly have severe cases and she doesn't into overdrive everytime.
Additionally, Ran likes it when Shinichi solves cases. Just aside from sharing the sense for justice and morality, she simply loves to him solve the case and to see the expression on his face when he figures something out. That is a thing that makes her happy. So, why would go so completely nuts when he does it?
These are all things that fit Ran as well. Ran understands the danger, she grew up with it and lives with it. Ran is more than capable of getting Shinichi out of danger, as she demonstrated several times already. This state that you only say for Ai: worried, but not fussing is exactly the state I would imagine being in, if their relationship got serious. Also, Ran is completely capable of being his Watson. How do I know this? Because she has been his Watson several times over the course of the series already. Hell, even as Conan she regularly serves him as Watson.
When was the last time she's done that? In our time? Roughly ten years ago I'd guess.