Galium - yes, I have that marriage; but it is problematical.
If that Elizabeth Hardwick is the widow Elizabeth lack who married Thomas Whitney in 1790, then she was born before 1750.
The problem I have is that Thomas and Elizabeth Whitney who married in 1790 are the only plausible parents for my ancestor Thomas Whitney who was born circa 1799 in Kimbolton. Because of the water damage to the Kimbolton parish registers I have not (yet) been able to find a baptism record for him.
If that is right, then the only way to square this up is to accept that Thomas Whitney's mother was in her VERY late 40s or early 50s when he was born. Not impossible, I'll grant you - but not very likely, either, in the late 18th century!
If we assume that the census entries egregiously understate Thomas Whitneys' age then we can get it down to early 40s, I suppose, which is less implausible. But with the marriage of Thomas Whitney and Elizabeth Lack taking place in 1790, we're not going to get this birth into her 30s ... and even then we have to suppose that she was VERY young when first married.
The alternative (which can JUST be fitted in to the available time scale) is to suppose that the Elizabeth Lack who married Thomas Whitney in 1790 was the widowed daughter-in-law of the James and Elizabeth Lack who married in Great Staughton in 1766.
It's all very unclear, just at the moment ...