Yes, if she can bring in a supply, it would certainly be beneficial for the baby to get her breastmilk! ESPECIALLY IF ONE OF THE MOTHERS SMOKES!!! I would suggest you talk to a local La Leche League leader (there is info about inducing lactation in the Breastfeeding Answer Book), and to go to asklenore.com for a GREAT protocol. And, no, it's my understanding that her breastmilk would be JUST FINE, as long as she produces enough. And, asklenore suggests that the inducing mother just start on the protocol asap, and then starts pumping and saving up every single drop, so that if she has to supplement, she can acutally supplement with her own FROZEN milk, rather than formula. If the expectant mother would be willing to, the BAB talks about a study that was done where the birth mothers had AIDS, and fed the babies their own milk, until the adoptive mothers could bring in a full supply, which all but ONE did, simply by putting the baby to the breast ten times a day. If the now pregnant mother was willing to nurse the baby just until the second mother could bring in a supply, it might work very well. Since they live together, this shouldn't be an issue, especially if the non-expectant mother had already been doing the asklenore protocol for some time before the birth...it would be within the realm of reason to believe that she could bring in a full supply.