Neighbor claims water damage from my unit

[Phil B.]

We own 2 units in a 4 unit townhome.  Neighbor emails me today stating that water from one of my units gutter has caused damage in her unit.  A bit more info - Last month I replaced the roof on my two units (end unit and 3rd of 4 units).  The complaining neighbor decided at the last minute she could not afford a new roof so opted out.  These town-homes are 15 years old and are in need of new roofs throughout.   We experienced leaks so replaced the roofs promptly.

Neighbor contacts roofer last week and tells him he installed the flashing along our shared roof line improperly.  We hired a well known, quality company.  They showed up the next day, unbeknownst to me and conducted a full inspection and found nothing wrong with their install.  They did notice the gutter, in their opinion, could use an extended flashing from the gutter lip up the neighbors siding that is in direct contact with our shared wall.  So they made this modification.

She now wants me to pay to repair her siding and the water damage inside her garage and guest bedroom.  Having never experienced this type of issue, what should I do next?