Shouldn't that be "she is taller than I"?

No.

She is taller than me.

She is taller than I am.

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https://dictionary.cambridge.org/grammar/british-grammar/comparatives-and-superlatives/comparison-adjectives-bigger-biggest-more-interesting

Comparative adjectives: using than

We use than when we mention the second person or thing in the comparison. If the second person mentioned takes the form of a personal pronoun, we normally use the object form of the pronoun (me, you, him, her, us, them):

Could you carry this? You’re stronger than me.

Not: You’re stronger than I.

Why did you choose Robert? Marie is more experienced than him.

In more formal situations, instead of than + object pronoun, we can use than + subject pronoun + be:

You managed to answer the ten questions correctly? Well, you’re definitely cleverer than I am!

I preferred Henrietta to Dennis. She was always more sociable than he was.

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https://www.lexico.com/en/grammar/comparative-and-superlative-adjectives

The comparative form is used for comparing two people or things:

He is taller than me.

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