breasts are dry, cracked, itchy and have water type blisters

cancer is probably not a concern yet, but let dr evaluate
does she have other health problems such as gastrointestinal gas, bloating, diarrhia, constipations, OR rashes, yeast, vaginosis because skin problems r just indicitive of somehting else and it does not mean serious somehting like cancer
good luck and if u don't have a dr. any quick care type clinic will do

Most likely that she has psoriasis and would need to massage her breasts with some very good body cream. This should be done daily for a couple of weeks and than twice a week.
She should also be watching what vinegar substance and acid meat she eat. Too much, her skin could secrete it through her skin thus, causing this dryness, itchy, cracked skin. If she fallow this, she will get a very lovely skin on her breasts.