[little lexi]

I am not a breeder just a pet owner and I have a question, my Lexi just went into her first heat, now she has swollen nipples is that normal? She has not yet been spayed as we only have two girls and one 12 week old puppy thats a male. Hes being fostered here does not live here, I am just a little confused as to why herr nipples are swollen, she will be to the vet first of the week if this is not normal...Thanks in advance..