Moderator, Iberia Airlines, Airport Lounges, and Ambassador, British Airways Executive Club
Join Date: Feb 2010
Programs: BA Lifetime Gold; Flying Blue Life Platinum; LH Sen.; Hilton Diamond; Kemal Kebabs Prized Customer
Posts: 63,811
INV basically adopts the standard BA terms here, with very few differences to a BA lounge. Now your post wasn't entirely clear, but as I understand it:
you = INV-LHR-CPT
spouse = INV-AMS-LHR-CPT
If so, her next flight from INV would be on KLM which means there is no access, unless she gets access as a KLM status or business class passenger. As you say, you can pay for access to Inverness separately, or do it in advance online. Weigh up the cost of that with the KLM version of POUGs, which to my mind are more readily available than the BA version. You should get the offer when KLM OLCI opens, assuming it's a straightforward INV-AMS-INV ticket. KLM's OLCI starts at 30 hours to departure. For NCL and MME to AMS the KLM POUGs cost around 70-80€ each way. The lounge also accepts Priority Pass.