"When do we get to meet your sister?"

In this context, "get" means "to have the opportunity to"

It is a common usage in english! Another example is the expression "get to know (someone)", which means "to be able/ have the opportunity to know a person"

"Im looking forward to getting to know your mom!"

"You just won't believe it! I finally got to meet my sister's friend."

"What do you do when you want to get to know someone? Well, you know, sometimes I just go out at night and try to make some friends!"

These are some examples! Hope I've helped you!

The phrasal verb get to is very common in English. The meaning of ‘Get’ in this sentence means have the opportunity to meet.

It means 'have the opportunity to meet'. It's a very common use of 'get'.