I have been puzzling over Jane Gawne. It appears she was buried 26 Nov 1864 aged 87 giving birth date of 1777. There is no Jane Gawne recorded for this date from Rushen, the nearest is Jane d/o Stephen Gawne & Jane Corrin chr 1777 Douglas.
Looking through other family connections and other families in the Corvaley/ Glenchass/Howe area I have a feeling that looking at the will of Ann Gawne als Crejeen 1820 might be useful. Henry Gawne and Ann Crejeen had a number of children who married and resided in the area. There is no Jane recorded for them but there is an Ann chr 1776.
That's all I can suggest at the moment. I could be way off...I often am...but it's worth following up if you want to pursue this.