Males "come into heat" slightly before the females do.  If he bred with her
then her swollen vulva would have gotten smaller.  Since she is 5 years old
and has never had a litter before it may be to late to breed her.  If she
has an open pyometra then yes one can use Lutalyse (prostaglandin F2alpha),
and an antibiotic (Baytril and/or Clavamox ).  You do not want to use
Lutalyse with a closed cervix pyometra.
 
Hard to tell for sure if it is a pyometra, but the green discharge makes
it likely.
 
Hope that helps,
Jerry Murray, DVM
[Posted in FML issue 3411]