。
She's even more beautiful than that.
Literal
She [topic-は] even-more more beautiful.
An emphatic stack: さらに ('further, even more') and もっと ('more') are both intensifiers, and combining them piles on the comparison — closer to 'even MORE so' than either alone. The sentence implicitly compares against an unspoken standard, often something just mentioned in conversation. Common register for expressive speech and writing where you want to underline that the subject exceeds an already high benchmark. 美しい (utsukushii) is more elevated than 綺麗 (kirei); both translate as 'beautiful' but 美しい has a more aesthetic, considered weight, often used for landscapes, art, and people whose beauty is striking rather than simply pretty.