To people having problems with this questline follow this progress route:
First encounter: Talk to her in Road of Sacrifice.
Second encounter: BEFORE Abyss but after defeating Deacons, she'll appear in Firelink Shrine. Talk to her there.
Third encounter: Talk to her in Catacombs.
Fourth encounter: Talk to her in front of Wolnir boss room. After doing this progress to the Smouldering Lake and kill Horace.
Fifth encounter: Church of Yorshka. If you are following Usurper ending, then this is where her personal questline ends.
Sixth encounter (non-Usurper ending) - You can go to her world and defeat Aldrich in Anor Londo, summon sign is just at the top of the stairs near the two Silver Knights.