Ferric ammonium citrate is widely available, relatively inexpensive, and
unless one was absolutely certain that the cause of Judy's current problems
is indeed some variant mode of manufacture resulting in a variety that
doesn't work properly for photographic purposes, the only benefit to making
your own, assuming every step involved was perfectly safe, and could be
precisely repeated, might be to ensure it really is the same stuff every
time, and therefore behaves predictably.
A good way around this is not to use ferric ammonium citrate at all - Mike
Ware's wonderful new alternative photography pages have his new cyanotype
article at http://www.mikeware.demon.co.uk/cyano.html
Philip Jackson
PS I've been meaning too but haven't got around to testing whether a citric
acid wash brightens the blues of a conventional cyanotype as well as it does
new cyanotype.