I believe the above would be

iníon an chroí

and "My daughter of the heart" is

m'iníon an chroi

But I'm not sure what "Daughter of my heart" would be. Possible

iníon de mo chroí

That last one doesn't feel right. Any thoughts??

m'iníon an chroí is wrong. I'm not quite sure what you mean by "my daughter of the heart". Would you explain what you mean by it? Something like "m'iníon den chroí" would be a literal translation that may work depending on what you mean by it. Definitely wait for more on that though.

Daughter of my heart would be Iníon mo chroí

I can second that

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I'm not a native (or entirely fluent) speaker, so be sure to wait for confirmations/corrections, especially for tattoos.

I'm trying to refer to a friend's daughter that I love like she's my daughter.
That last one, "iníon mo chroí" sounds like what I wanted.
But why would "m'iníon an chroi" be wrong?? Would that actually be "the heart of my daughter"??

It is grammatically impossible.
Both mo (m’) and an chroí would refer to iníon. This is impossible in Irish.
In English, "my daughter of the heart" is grammatically permitted, but not so in Irish.
Every noun can take only one possessive ("mo") / definite genitive attribute ("an chroí"), not two or more.
Both "mo" and "an chroí" are ways to make the noun "iníon" definite (my daughter / the daughter ...), but only one way is permitted, "my the daughter ..." doesn't make sense.

In English this phrase is to parse as [my [daughter of the heart]]
In Irish "m’iníon an chroí" would be parsed as [mo [iníon] an chroí] -> obviously nonsense.

So, iníon mo chroí (the daughter of my heart) is the best alternative.

Ok, thanks all.
Seems like iníon mo chroí is the winner.
But is the exact translation "daughter of my heart" or "THE daughter of my heart"??
Both have been given as the translation is this thread.

A true artistic masterpiece!!! Chugam aniar thú, a Labhráis!!

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If you wish to say "my daughter of the heart" the best you can get may be:
m'iníon croí
or god forbid
mo chroíníon
how wild!! hahaha I feel indecent having written something so crazy

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