i think they mean the hairless girl is shy and it wont get better...
at least thats what i got from the way its posted, though its definatly hard to put together...
i think in the right hands the shyness could be gotten over, cresties are definatly a "special" breed in terms of being prone to standoffishness and need some extra work, as do chihuahuas of course...
there gonna make someone wonderfull pets.
it could mean size though, at 6 months there about done growing height wise and being female they wont "fill out" much either.
did they get back to you about a rehoming fee yet?