Sorry am going to give a predictable Mumsnet answer here, but I am wondering if your dd struggles with other social interactions or has any other traits that might point to something like aspergers? To be clear, no expert on this, but I am wondering if there’s something else going on underneath?
Maybe just a non demonstrative child though or finds direct displays of affection too much...
On that lighter note, my DS would say ‘I love you’ to his grandfather & daddy, but when I said it to him he’d look confused and reply ‘well I Like you’ and turn away.
I tried to be all sensible and ok with it, but it did hurt. Went on for a good couple of years.
Eventually I saw him do the same to my mother, and it slowly dawned on me that Ds wasn’t necessarily meaning it the way it sounded. In fact, he’d had made up an extra grammar rule!
He’d decided you say Love to males, and Like to females. He got cross when I wouldn’t say the correct thing to him, hence the cool answer and turning away.
Even now he loves a good clear rule with no exceptions or deviations!