AIW to tell my (20F) best friend (18F) that she’s a rebound?

I’ve been debating telling her this for a few days now and I’ve been asking everyone’s opinions so please leave your thoughts. (Names are changed for privacy)

I (20F) have a best friend (18F) who recently got out of a long term relationship about a month ago. This relationship was not the healthiest and after they broke up I spent a lot of time helping her heal from the pain of losing someone that had been in her life for so long. About a week ago, a previous talking stage of hers, Logan, got out of his year-long relationship. During this relationship, my friend, Emma, was blocked on all social medias per the request of Logan’s now ex-gf. Emma found out that they had broken up via a friend of hers (with the same name) who is the ex-gfs roommate. The roommate heard the ex-gf hooking up with another guy the day after the breakup and recorded audio of it and sent it to Emma. The next day, Logan unblocked Emma on Instagram and they began to talk. A few days later, Logan and his friends met up with Emma and I at a line dancing bar that we frequent. At the end of the night, we all went to grab food and I went home. Emma and Logan went back to Emma’s and talked until 3-4AM. This started a consistent cycle of them either talking in person, over the phone, or texting until 3-4AM every night. During one of these chats, Logan brought up the fact that he might be interested in being FWB with Emma. Emma took this as him saying he is still interested in her while I took it as him saying he wants someone to hookup with. Side Note: Emma and Logan have had an on-off flirting thing for a long time and Logan always gets into a different relationship and blocks Emma. From what she’s told me about their previous endeavors, she has always been the second choice to him, until someone better comes along. The following Wednesday (this past Wednesday) they had plans to hang out. Logan goes to Emma’s house at 9pm and they spend the whole night talking, except this time they end up making out and he feels Emma up a bit. They’re up until 6AM before Logan leaves Emma’s house. Emma and I were supposed to study that day, but she ends up sleeping most of the day because she had been staying up so much to talk to Logan.

I find it suspicious that he is already ready to jump into something new with someone else after being broken up with only a week ago, and her being in a fragile state after her 5-year relationship ended only a month ago. I’m happy that she’s been doing well since they first started talking but her ex is still very prevalent in her life and I don’t want her jumping into something with the premise that it will lead to a relationship as it seems he’s only interested in hooking up.

Do y’all think I should tell her? If so, how do I do that without making it seem like i’m trying to take away her happiness?