UPDATES:
Human reinforcements are a full defense fleet, so a battleship, multiple heavy cruisers and lots of escorts. If this fleet arrives, the aliens will need to flee or be wiped out
In system, humans have this frigate, and a handful of cheap fightercraft that won't do much.
The aliens have encountered a few human vessels, and are aware of the fact they have shields. They are not aware of the human reinforcements, or which jump point any reinforcements will come from.
In case it wasn't clear above, the aliens do not have FTL sensors in any way. They are entirely reliant on the speed of light for their sensor data. They also do not have FTL communication
Alien motivations are decimation. They see this system (and perhaps others) as theirs and they will cleanse it of human presence, with a later goal being colonization.
How would this battle play out?