Bestfriend and obsession

Ok well its not a big deal but im worried for her, cause she just doesnt stop :/, My bestfriend had fancied this boy when we were 11-12 years old, and well I would describe her as obsessive, and a stalker :/, well she fancied him like for a yr I think then she started liking other boys.

And now were 15 shes not obsessive anymore, she doesnt do the stuff she used to do when we were younger, she used to follow all of his footsteps and touch everything he had touched and just gaze at him all day when we were about 11 or 12, but now she learned from that and I must say im happy she did, but recently she fancied this boy “M” for like 3-4 months and like she found out things about him by her own sister, and she told me stuff that is personal about him and the truth is that I found it quite freaky for her to know those stuff without him telling it to her in person :S Well tbh I never fancied anyone like she has, I don’t go asking my brother to get information about him and tell them to me, I go and get to know them in a normal way. My bestfriend and “M” arent that close they dont even talk to each other, and if someone came up to me that I didnt know and knew everything about me I would freak out, now my bestfriend are trying to get over him and now she puts her affection on someone else and im worried she puts her thoughts into this other boy and even go further than she already has :S

any advice what I should do, is this even normal??? I hope it is.