I found your request whilst surfing and I have registered with this forum in order to respond to your post regarding Princess Helena Davidovna Palavandova. I am the grandson of her husband and I can be seen pictured in the 'Daily Mail' article.
I am sure you are interested in historical fact as apposed to family legends so here's a few facts you can check yourself.
1. I can post a copy of their marriage certificate if you wish (which shows her rank, and that of her father).
2. I have discovered much by means of a little understanding of the politics, history, and languages of Georgia. Despite her marriage certificate naming her as 'Helena', it is much more likely that 'Elena' would a more accurate translation. The Russian version of her family name can be seen translated as 'Palavandoff' as well as 'Palavandov', and the Georgian version of the family name is 'Palavandishvili'. If you search using the Palavandishvili spelling you should come across a scholarly article in Wikipedia which describes the family's heritage and status. You should also find mention of several Palavandishvili Princes in historical texts (on-line) which describe their involvement at key moments in Georgian history.
3. The politics of Georgia are as complex and sensitive now as they have always been, it seems that Helena's grave was not marked at the request of the 'British Authorities' for complex political reasons here. Despite continuing issues in Georgia, we felt that here in the UK folk could now react to a Princesses gravestone in a mature manner.
4. Our family are continuing to research this family (with limited success) and any substantive facts I will happily share.
I hope I have been of some assistance.