We’ve seen Claire with a hint of grey in her hair and an older daughter.
We’ve seen her pregnant in Season 2 and trying to explain to Frank exactly where she had been.
Kudos to the makeup team for the work they’ve done, but from what Caitriona Balfe said at the most recent Comic-Con panel the bigger challenge for the actors is not looking the part, it’s understanding a character’s frame of mind across decades that’s the hard part.
One of the challenges with filming Outlander is that the series hops around quite a bit, not only between the 18th century when Jamie is living and the 20th century where Claire has returned, but also between decades.