Am I over reacting about this?

recently my best friend got two books that ive been working my a** off for. i told her a while ago that i was planning on gett them. and then she went out and got them. when i asked her about it she said that she forget that i had wanted them even though i had told her. i then ask her if she knew my age( i just asked this in a joking way, to see if she had maybe forgoten my name) well she did forget it, she guessed 2 years completely off of my actually age. i then figured maybe i just hadnt told ppl and thats my BEST friend( who've i known for 7 years!) didnt know my age, soo i asked some ppl who i dont really hang out with and ALL of them knew my age and said it immediatly. what does this mean? is she really maybe just clueless and forgetfully? or is it something else? oh and just so you all know, the reason y i dont just go out anyway and get the books is because she hates it when ppl get the books she already has, everytime on of our friends get the same books she has, she has a meltdown, and wont talk or hang out with them for a week or two.