What does “in camphor” mean?
Camphor is used (among other applications) as a repellent against moths and other insect pests.
So I take the mention of 'retirement in camphor' in the extract you cited as a somewhat laboured reference to the fact that for nine months of the year, the author's foster-motherhood was 'in mothball storage'.
Her comment that during the three months of the year in which she was actively involved with her foster children she would replenish their wardrobes subtly encourages or emphasises this interpretation.
It's another way of saying "mothballed"