Once Holy Knight Hodrick is dead, return to Firelink Shrine and speak with Sirris to accept her loyalty and then travel to the Pit of Hollows bonfire to collect the Sunset Armor Set near the Mound-makers altar.
You can now return to Firelink Shrine and exit the arch on the second level, follow the cliff on the left side to the area with the Grave Warden overlooking the edge, and pick up the Sunset Shield from the tombstone.
Note: While this is not the end of Sirri's quest, the only other item obtained is the item she drops upon death. This means that the only reason to keep her alive would be for aid in future boss battles as a White Phantom.
For this reason we'll now progress with Ringfinger Leonhard's quest and the Rosaria's Fingers covenant.
Travel to Rosaria's Bed Chamber in Cathedral of the Deep and finally join the Rosaria's Fingers covenant, making sure to offer her at least one Pale Tongue.
Doing this will cause Ringfinger Leonhard to move to this area, where you can speak with him, and also force Sirris to appear in Firelink Shrine, where you must kill her to obtain the Sunless Talisman.
Return to Rosaria's Bed Chamber and collect the Black Eye Orb from Rosaria's corpse and then make your way to Gwynevere's chamber at the top of Anor Londo's boss room. Here you can use the orb to invade Leonhard's world and defeat him for the Soul of Rosaria, Crescent Moon Sword, and Silver Mask.
Note: The Soul of Rosaria can be used to revive Rosaria, but this is pointless since you can give covenant items without her being alive and the soul can be transposed into the Bountiful Sunlight spell.