My sister said she’s nonbinary and i don’t believe her

My sister just came out as nonbinary. But the way she did it was very weird. She just randomly out of the blue said “I’m not your daughter don’t call me beautiful”. Bc my mom complimented her. And we were like.. huh? And she then said she’s nonbinary and has to be referred to as they/them. I’m VERY accepting of this. I’m bisexual. I’m apart of the community. I would never question her about this but somethings wrong. Literally a week ago she downloaded tiktok and saw a video tagged nonbinary. She asked me what it meant and I told her. She laughed and said she thinks one of her friends is. She had no clue what it was. Then randomly today she said she’s known she’s nonbinary for MONTHS. And I’m like how tho. And she’s like it’s none of your business. She’s also fully supportive of people who fake sexuality’s and genders for attention. She thinks it’s okay bc they have the right to. I honestly think that’s what she’s doing. A month or so ago she confided in me that she wishes my parents gave her more attention bc there’s 7 of us kids and attention is not spread evenly. She pointed out that she sometimes acts out for attention and I told her I knew she did that and she needed to stop. That’s honestly what I think she’s doing. She’s also still calling herself she on her snapchat but when someone else says it she gets very defensive. And it’s just a mess. If she’s nonbinary of course I will accept her. But I genuinely don’t believe she is. I don’t know what to do. One of my close friends is nonbinary and i told them about this and they said that they don’t believe my sister is nonbinary. And that it’s just very weird how this all happened and the events leading up to it. Idk I’m just ranting but idk what to think.