The 36-year-old actress – who has played Sienna since 2012 – thinks her on-screen character has become “desperate” in her bid to keep Brody Hudson away from Summer, played by Rhiannon Clements.
She told Metro.co.uk: “She’s such a pain for Sienna! Obviously, this girl has just shown up at a very inconvenient time, and she seems to just always be there. And now Brody thinks she’s super, but Sienna has this really strong instinct that everything is not as it seems, which I think the audience are already in on – they already know Summer is up to something.
“Sienna is very frustrated. She’s desperate to keep Brody away from Summer, but of course it just reads like, ‘Oh, I don’t like your new girlfriend’. But Sienna’s like, ‘No, there really is more to it than this, and I know because I’ve been that girl, and you have to stay away from her!'”
The issue comes to a head this week, when Sienna is left in a serious condition after being shot by Summer.
And Anna thinks the storyline has been developed in a really interesting way.
She said: “The perspective that we’re telling the story from is that the audience are in with Summer and they know what she’s up to, but they know that Sienna doesn’t know, and they’re waiting for her to catch up as to what’s going on.
“I think that makes the story all the more interesting. So far, Sienna has just seen Summer as a bit of an inconvenience, but I don’t think she’s quite seen the darkness that can come from that, so that’s going to be good when the penny drops.”