Not an expert, but I would suggest that her faeces may contain scents that will advise males that she is coming into season, so she is 'advertising' in advance.
Because she will want to mate somewhere where she knows she is safe - again survival instinct - she will advertise on her home territory, so the males come to her there.
Unfortunately, her 'home territory' doubles as your house!
It's doubtful you can train her out of this - it's primeval procreation instincts at work - but if she is prone to use the same spot or area, cover it with newspaper.