the low and high beam share the same ground, so if the high beam is working than the ground should be fine. you can test this with a voltage drop test, bit im pretty sure if the ground was bad than the high beam would not function.
the ground for the right headlight is located on the right side of the engine compartment.
there should not be 2 blacks and 1 green wire there unless the connector pigtail was replaced at some point.
there should be a black wire, which is ground
a light green and black, which is the high beam 12volts.
than a white with light green trace which is the low beam. this is the one that we need to focus on.
this should have 12 v when lowbeams are on.
fuse 4 is the right low beam fuse. if the fuse is ok, and there is 12v there, than there is a open wire between the interior fuse box fuse #4 and the headlight connector.
the harness will have to be opened from the 2 points to locate the open fuse
also, check at the back of the fuse panel to see for loose connection there too as this is common.
i have included a wiring diagram for your reference.
let me know what you find and we will go from there