Even then, being spoiled wouldn't necessarily give her that utterly nonsensical view of love. Wouldn't she see the love her grandfather gave her and take some inspiration from that, think spoiling him is love. Yet somehow it instead somehow it turned into this ridiculous over the top abuse. I need some more backstory because this is nonsense.
It might be a different story if you consider how her grandmother treats her husband, very toxic-like, and being the same sex as her, as opposed to her grandfather who, as a man, spoiling a female he loves is natural, and she could very well misinterpret MC's servitude towards her up to high school as his way of 'spoiling' her.
Daughter sees mother-figure degrading her father: "I see! So that treatment to someone you love is normal! I shall do the same to my crush!"
Monkey see, monkey do. A lot of parents don't realize how influential they can be to their own children.