My(18M) girlfriend(19F) of 1 year wants a seemingly random STI test after we had unprotected sex. Why would she now want a test after all this time?

My(18M) girlfriend(19F) and I had unprotected sex about 2 weeks ago, and I've now learned that she's wanting an STI test.

We've mostly stick to condoms due to us not ever wanting children, but we've had unprotected sex before, and at those times she's shown no worry about STI's and has never brought it up or mentioned it before.

She's said many times that she has no concerns about me cheating or being unfaithful, she's my first girlfriend and sexual experience, and as far as I know, STI's can't come from 2 partners who don't have one.

Does she not trust that I'm clean for some reason, or is worrying about STI's from your partner a normal concern in relationships?