expression, suru verb (irregular)
to love one's child too much for their own good; to love one's daughter so much as to make her a nun
Rare, literary set phrase. Literally 'to love so excessively that one makes (her) a nun', used hyperbolically for overindulgent parental love that ends up harming the child. The literal nun reference is part of the fixed expression.
「寵愛昂じて尼にする」とは、子供を甘やかしすぎるとかえって不幸にするというたとえだ。
'寵愛昂じて尼にする' is a saying that spoiling a child too much will only make them unhappy in the end.