13 month old doesn't play anymore with new kitten

(Can't edit title... meant to say she doesn't play with us).

I have a 13 month old female who recently got a brother.  They get along well and play together, running around a lot.  The kitten loves to play with us but now the 13 month old doesn't.  Is that normal?  Should I be doing something to encourage her to play more or is it just that she's getting all her energy out with her little brother?

This is normal, and as long as it doesn't bother/offend you personally it is also fine You will probably find that when the 'novelty' of having a playmate wears off she will be more interested in playing with you as well again. Some cats also naturally begin to 'quiet down' a bit around one year, though of course they still are very young and have tons of energy- it's possible she is using a lot of her energy just keeping up with the kitten 

Congrats on your new addition and no worries, all sounds normal, even ideal- sometimes cats don't end up getting along and that can be sad for everyone- how lucky for you that they are best friends