Laurie -- In the long run, breast feeding does lead to permanently enlarged breasts (for most women).   And whether mom breastfeeds or not, she will still go through the prolactinization at delivery, with a subsequent growth and engorgement, which will pass in three days to a week, with or without the comfort measures we discuss at such length on Lactnet.

Of course, if mom has gained a lot of weight, and that is the cause of her increased bra size; and if she doesn't lose the weight again, her breasts may stay larger.

I would encourage her to think about breast-reduction surgery long after she has finished breastfeeding, if ever.  She may have another child, and still need the original pair.

Sincerely,  Chanita, San Francisco