It sounds selfish, but I don't want my girlfriend to star in a movie
A movie might be fun. Why don't you want her to star in a movie?
Because people would judge her because she's terrible at acting after all.
You really shouldn't hold your partner back. She wants to be in a movie, so support her dreams.
She's worse than Halle Berry and that's saying a lot.
Maybe keep that opinion to yourself, and stop discouraging her from doing this is she wants. Think of how happy she will be when she thinks that you support her. She might even be better than you think, and you could get a surprise.