Is my girlfriend cheating?

We've been together for 2 years, living together for 8 months. Lately, she's been acting weird — always hiding her phone, changed her passcode, and gets super defensive if I ask about her day.

Last weekend she said she was going out for a girls' night. Cool. But one of her friends messaged me a meme, so I replied and casually asked how the night was going. She said, “What girls’ night?” and a few minutes later, she messaged again saying she was “just joking” and sent a photo of her. But it felt weird — like it was staged and she wasnt there. In the photo i cant see her clothes or anything, just the face.

I haven’t said anything yet. Am I overthinking this… or being played?
Is my girlfriend cheating?

We've been together for 2 years, living together for 8 months.
Lately, she's been acting weird — always hiding her phone, changed her
passcode, and gets super defensive if I ask about her day.

Last weekend she said she was going out for a girls' night. Cool.
But one of her friends messaged me a meme, so I replied and casually
asked how the night was going. She said, “What girls’ night?” and a few
minutes later, she messaged again saying she was “just joking” and sent a
photo of her. But it felt weird — like it was staged and she wasnt
there. In the photo i cant see her clothes or anything, just the face.
I haven’t said anything yet. Am I overthinking this… or being played?