Is there a psychological trick to know if a girl is interested in you?

1. Look at her pupils
Elevated oxytocin levels increase eye-gaze and creates a sense of well-being that increases attraction. This hormone is responsible for creating close bonds. Oxytocin also dilates the pupil up to three times the regular size when you see something exciting or interesting.
If she's attracted to you, her pupils will get bigger.

2. Mirroring
People who like one another, copy each others gestures and body language without noticing. If you are with her, try changing your body position. If she likes you, she'll follow you.

3Check her toes
A woman's body language is more than fiddling with her hair. If she likes you, there's a chance that her toes will be pointing towards you. If she likes you, she'll lean in towards you whilst talking. If her feet is crossed, that's a bonus. [1]
When someone is uninterested, their feet generally don’t point towards the person with whom they’re speaking. Their feet point away, and only their torso is facing their conversation partner. This prepares them for a quick exit.

4. She texts first
Not all women wait for a text. If they are genuinely interested, they'll text first. However, if you've made the first move, do not spam her. Leave it at the one text. If she likes you, she'll put in the effort to reply.

5. Does she ask you personal questions?
If she remembers the small details and asks you questions about your life, that's a clear sign that she's interested in you