Endometriosis therapy includes
1)  Birth Control pills
2) Medroxyprogesterone(Provera)
3) Danazol(antiestrogen, androgen)
4) etc.

Progestins have been used for years to control endometriosis,  as they stop
the proliferative phase of endometrial growth.  Of these above therapies,
higher dose Depo Provera might help this mom and permit her to continue
breastfeeding.  She could ask her gynecologist about this therapy.  Some say
it depresses lactation,  others not.   But it is better than the
alternatives(danazol) for a lactation mom.

tom hale