During family conversations my sister, who is 27, often interrupts the flow of a conversation with in order to mention something that is marginally related to the topic at hand. Most of the time this falls flat; as what she's talking about isn't particularly interesting, related or something the group she's talking with understands. I'd say she is a "nerdy" type and will often bring up various forms of media that the family isn't familiar with.
Family A: Did you see that ludicrous display last night?
Family B: What was Wenger thinking sending Walcott on that early?
Family A: The thing about Arsenal is, they alw-
Sister: Did you guys watch the latest episode of Arbitrary Niche Nerd Media? It was really cute when Character A kissed Character B!
Family A: I really don't know what that is?
(awkward pause in conversation)
Family B: (topic change) Oh man, did you guys hear about Stacy?
I know this is a rather contrived "example" of how she acts, but I'm really trying to emphasize her poor timing and how these situations play out. Even if I try to play off of what she says, it almost always ends in an awkward pause and someone bringing up a new topic. I'd also like to state that in this scenario, my sister is well aware of the ludicrous display last night, so it isn't a lack of understanding of the topic.
Personally I find this really frustrating as it often derails a good conversation. It's apparent to me that my family appears to feel the same way based on their body language/facial expressions. I don't want her to stop participating in conversation, but I want to bring it to her attention that the way she's communicating is generally not being received well.
I personally am familiar with the things she talks about often. She talks about games and shows that I've watched or know something about. The issue is a combination of the timing of her interjections and her (seemingly) not understanding her audience. It really isn't a matter of getting to know her better, but a matter of letting her know that mentioning X concept from Y media where my family doesn't know anything about X or Y is a distracting conversation topic especially when it's provided with very little context.
The Interpersonal Problem
My sister is rather sensitive (she doesn't have diagnosed mental health issue) and telling her outright would most likely make her just not want to talk or socialize at all. It's not my intention to upset her, or exclude her from wanting to participate. So how can I tell her that the way she interrupts/detracts conversations has been typically hurting the conversations she's be involved in a way that doesn't hurt her since she doesn't seem to be aware of the way she disrupts the flow of conversation. This is a request for techniques on softening the blow of a revelation that may not be well received.