。
She weighs 120 pounds.
Literal
She [topic-は] body-weight [subject-が] 120 pounds exists.
The construction Xは[measurement]ある is the standard frame for stating a measurement, where ある ('exist') functions as the predicate carrying the measured quantity. Pattern: [topic]+は+[quantity]+ある. Used for length (この紐は3メートルある 'this string is 3m long'), weight, distance, etc. Note that the use of ポンド (pounds) is unusual in Japan — kilograms are standard for body weight; this sentence implicitly sets a non-Japanese context. Arabic numerals are also typical of Japanese with non-traditional units.