I'm not sure if I would be of much help, but I just wanted to highlight that I'm struggling with this too as everyone I've met from
Cooley has been contagiously lovely which makes me want to apply but I'm personally not really interested in their sectors so it's a challenge to draw any personal link to the work they do.
It is ultimately an Open Day and the point is very much to find out more about them so I wouldn't worry too much about focussing more on one sector. However, do also try and sprinkle in some amount of "why law" given your non-law background because this is probably an implied part of the question too.
I would say that it's great to highlight your interest in the life sciences sector, maybe look for specific clients and deals which you can relate to (remember to be as specific to London as possible as well) on their website, Legal 500/Chambers, or the many profiles out there (Legal 500 Future Lawyers/Chambers Student/Legal Cheek/
TCLA). It might also help you identify if there's a specific part of the market they operate in e.g. listed companies, emerging companies, mid-high value companies etc.
You could also cover their small trainee intake and how it translates to collegiality, early responsibility, and more on-the-job training too. I know they're very active in the VC space and work directly with many founders too so if there's something that you could link to that, I think it would be good.