Sometimes girls flirt with guys, and sometimes girls flirt with girls. Not surprisingly, flirting techniques are pretty universal, whether someone's flirting with a girl or a boy. If you're not sure whether a conversation between two girls is friendly or flirty, there are signs to determine the difference.
Consider their relationship. Sometimes, close friendships between girls are mistaken for romantic relationships. If you know the two girls are close friends, it's less likely that one of the girls is flirting.
Watch for body language. The next time you see the girls interact, look for signs that they're into one another. Are they leaning in close to each other? Making eye contact and smiling? Is one girl casually touching the other on the arm or shoulder? These are classic flirting moves.
Listen to their conversation. Are they complimenting one another? Making plans to meet up? Laughing a little too loudly at one another's jokes? These are examples of flirty conversation. In contrast, talking about subjects like work or school tend to be less flirty and more friendly.
Ask her. If you know the girl well, don't be afraid to casually ask if she's flirting with the other girl. Be open and friendly but don't push, as she may not be comfortable discussing it. If it turns out you were wrong and she gets offended, apologise and explain your reasoning.
There's no sure-fire way to tell whether a girl is flirting with another girl unless you ask her.
Know your limits; don't eavesdrop on a private conversation or snoop where you're not welcome. Never judge, discriminate or stereotype. Girls are free to flirt with whomever they want. Don't start rumours or spread gossip about either of the girls.