NOTATIO

Sorry, I was a bit unclear! The last six notes doublestemmed is indeed an error. As for sliding with index finger: it would not work as you would slide with your fingernail. Think harp is played with "two left hands" so thumb is always the highest finger (and little finger is never used). ...

Yes, the high C# to B is played sliding the r.h. thumb - a standard technique on harp. But the last six notes are divided (depends how the passage continues), maybe 4+2 to right and left. In slower tempo those six notes could be played with one hand, like one uses in piano playing "finger over ...