The word Freundin can mean either a girlfriend or a female friend. In some cases, they can be distinguished by using the possessive pronoun to refer to the former:
Ich habe mit meiner Freundin (girlfriend) gegessen.
Ich habe mit einer Freundin (female friend) gegessen.
Sometimes, though, this isn't possible. For example, how to translate these sentences?
-- How was your trip?
-- Great, I've met a new (girl)friend.
A drink for my (girl)friend too, please.
How is this distinction usually made?
When it is really very important to make the distinction, I might use:
eine Freundin von mir
In the restaurant situation, you might consider switching to
ein Glas Wein für die Dame hier
or much more frequently
Könnten wir noch ein Glas Wein haben?
and sort out the details when the wine is brought to the table.Tweet