Social Media, if a DNA Match has not been on sites like Ancestry or My Heritage for a while and are not responding to Messages then do hunt for them on all the social media websites.
As you have her possible name then a look through the Electoral Rolls will give an address, you may have to pay for this or physically visit the archive or library where the local rolls are stored. Once armed with an address you can write to them.
This is something I had to do fifteen years ago to verify I was on the right track with someone.
Now the 315cM and possible pedigree collapse complicates the DNA inheritance process and there is no easy way forward without the agreement of the match, unless they happen to have uploaded their data to Gedmatch which is probably wishful thinking. It is worth checking if they have uploaded their data though, not just to Gedmatch but to My Heritage and My Living DNA etc
Firstly action though would be to stand back and look at Debs’s tree and specifically I would print out a Pedigree Chart and mark on the chart where there is a DNA match that links to a specific MRCA or MRCA Pair. You can have all the documentary evidence for a specific person and a branch but unless you have DNA confirmation all the paperwork is just that documents, it substantiates a relationship but it does not prove it. Then looking at the chart you can see if there are no DNA relationship down a xGGP line hence that line itself becomes questionable.
As an example on my marked chart I have zero DNA matches linked from either of my Paternal Great Grandfathers or beyond them, hence there are probable NPE’s despite having all the BMD records etc and certificates.
If all is OK with Debs’s Marked Tree then there could be an NPE with Samantha’s line but getting the supportive documents could be highly unlikely.
