We thought it dangerous for her to go alone.

[bit]

Spanish Translation

Pensamos que es peligroso que ella vaya sola.

Is this structure common in English?

There a verb missing and it itches me.

[pitti42]

Look at wiktionary: think - Wiktionary, the free dictionary
It’s meaning #4.
If used like this, it’s the same pattern as “I find it dangerous” or “I consider it dangerous”.

[bit]

I was tired because it does make sense to me now
Thank you so much!

[Floria7]

I go with Pitti42 here.