Dear Mary,  I found a ref. in my files which might be useful to you.
 Wolff,M.: Occupationally Dreived Chemicals in Breast Milk. Am J Industr Med,
1983, 4:259-281.

It contains a general section on solvents, which is, I guess, the main issue
with your mom who is returning to work.  Here is a brief excerpt: " The
pharmacokinetic behavior of solvents is similar to that of inhalation
anesthetics.  Hydrocarbons and halogenated hydrocarbons are absorbed, mainly
through the respiratory route, with almost infinite uptake possible by
adipose tissue.  Upon cessation of exposure, excretion occurs (1) directly
via the lungs and (2) by metabolites in urine.  Depending on volatility,
respiratory excretion is usually complete within 8-24 hrs, although traces
may remain in adipose tissue.  However, compounds that are not readily
metabolized remain in the body in spite of their volatility.  For example,
tetrachloroethylene (PCE) is detectable in breath as long as 2 weeks
following exposure.  This commonly used cleaning solvent was the source of a
reported family exposure, where severe neonatal juandice was attributed to
ingestion of PCE in breast milk.  The father, who worked in a drycleaning
plant, had 30ug/mg (pmm)  PCE in blood.  Two hours after visiting him at
work, the mother had 3 ug/ml in blood.  Her milk had 10 and 3 ppm PCE i and
24 hours after exposure.  The infant recovered when breastfeeding was
discontinued."

What this says to me is that breathing solvents can be a problem, but I still
don't know the answer to the specific solvents you are asking about.  I saw
acetane in a table in another study  as a substance which had been detected
in mother's milk, but it didn't say what the effect on the infant would be.
Can she wear a breathing hood?

Hope this is somehow helpful.
Barbara Wilson-Clay, BSE, IBCLC