Janet, the "danger" of mom getting a tattoo would be if (1) she has the
design put on her breast near or on the nipple, or (2) unsterile equipment,
which would be a risk to her for disease transmission or infection regardless
of whether she is breastfeeding. Tattoos are skin dyes. They are poked or
scratched into the skin surface using needles. The skin has open wounds for a
while afterward, and must be cleaned carefully to prevent infection. I doubt
that the dyes go anywhere where they could affect the baby because the
designs stay put and don't spread. On what body part is she contemplating
getting her tattoo?  She should pick a reputable artist who uses sterile
equipment. (I'm not going to comment on whether I approve or disapprove of
tattoos. Not relevant to this discussion.)

Crohn's disease is a bad gut (intestinal) disease affecting digestion and
absorption of nutrients. Painful and debilitating, and a serious illness.
Artificial feeding is implicated in higher rates of this.