Learn French: La star travaille tellement qu'elle déteste la célébrité. - The star works so much that she hates fame.

In French, when you want to express that an action is done to such an extreme extent that it causes a result, you must use tellement que or tant que. You cannot use beaucoup que. Here, working so much is the intense action, and hating fame is the consequence.

Could I use tant que instead of tellement que in this sentence?

Yes! When modifying a verb to show a consequence, tellement que and tant que are completely interchangeable. You could easily say La star travaille tant qu'elle déteste la célébrité with the exact same meaning.

Is the English loanword star always feminine?

Yes, une star is always a feminine noun in French, even if the famous person being discussed is a man. Because the noun is grammatically feminine, the pronoun that replaces it later in the sentence must be elle, regardless of the actual person's gender.

Why is there a la before célébrité when the English translation just says fame?

French requires a definite article (le, la, or les) before abstract nouns and general concepts. When talking about fame in general, you must include the la. English usually drops the article for general concepts like this.