They wouldn't really be anything to you. She would be a cousin once removed by marriage only. She is your cousin's husband's neice but in no way is she your actual relative!
A precise term would be "cousin-in-law, once removed', because if you were to follow genetics(even though there are none in this case), then you would be your cousin's husband's cousin-in-law, and his sister would *also* be your cousin-in-law, and her child/daughter would be your cousin-in-law, once removed:
It's the same principle as your biological cousin's child...just with the "in-law" added.
Although by that point, a lot of people use alternate terms or don't even bother because they're so stretched-out & tenuous; especially through marriage ties, but even biologically, i know people who are referred to in this manner as "aunt", "uncle", "niece", "nephew" or just "cousin", etc...depending on age, closeness, familiarity, etc. A lot of times, that practise seems to be a way of bringing people and families closer together.
BTW: your child would be that daughter's "second cousin-in-law", just fyi :D.
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Unless your wife is also your cousin, your wife's cousin is most probably not related to you. The daughter would therefore not be related to you either, unless your wife's cousin was married to one of your cousins.
Your first cousin's daughter is your first cousin once removed. Your daughter and she would be second cousins.
Your first cousin's child is your first cousin, once removed. That child and your child are second cousins.
They are out of synch by a generation with the common ancestor. She would be a first cousin once removed.