@Yatsuki
Possibly, she's suffering from an inferiority complex with her husband's old lover who looks a lot like her daughter and she kept getting miscarriages that were really important to continue the male royal line. Deep down she probably scared that the love her husband gave to her husband is an extension of her husband's love to his old lover. She might want to change Tania's appearance to affirm her husband's love and escape from the shadow of her husband's old lover.
At the beginning, it says "My Mother ... became queen when she was 13 years old, and gave birth to me when she was 14." "Mother always loved Father. But it was an unrequited love."
Far too young, and never having those feelings returned.
Even by the end of the chapter when Tania is eight, that means mom is still 22. She strikes me as someone who, if she'd had less pressure and someone who loved her back, would still have been kind of ditzy, but not in a harmful way.