Break out your pen and paper boys and girls, you'll want to write this one down.
The first time I saw this, I thought it was a typo, it reads like something is missing:
Me perdí la reunión donde Clara
I missed the meeting where Clara
However, when my friend used it a second time, I knew there was something going on I just didn't understand.
It turns out donde has a colloquial usage I never knew about. In this context, donde means "en la casa de" or "en casa de". With that in mind, we could have written this as:
Me perdí la reunión en la casa de Clara
I missed the meeting at Clara's
Who knew? Let's go over a few more details.
When you say "donde Clara", you're refering to that persons home, regardless of whether they are at home or not.
Here's another example:
Estoy donde mi amigo
I'm at my friends house
Your friend may not be at home, but that's where you are. You can also use the construction "en lo de" to say the same thing.
Me perdí la reunión en lo de Clara
I missed the meeting at Clara's (house)
In a slightly different context, donde can also mean "next to" (‘junto a’ )
El banco está donde el cine
The bank is next to the movie theatre
This usage of donde in these contexts is pretty common and will make you sound like a native speaker for sure. I recommend you go and use it every chance you get to burn it into your memory.