If your researcher is in a location where she also has access to records from Caithness, it may be helpful to have her do a quick check in the records for Thurso, as it seems many Sinclairs operated out of Thurso as merchants. There isn't enough evidence pointing that direction to go on wild goose chases, but the following family may be one to check if she is in Edinburgh:
George Sinclair of Assery married Isabel Sinclair about 1660- Although the LDS records aren't totally reliable, these appear to be their children

- Alexander 4 Sept 1673
- John 15 Aug 1672
- Robert 23 Jul 1677
- William 22 May 1661
- James 2 Nov. 1675
- Francis
- George
- Elizabeth- does she marry an Alexander Sinclair?
- Patrick