Formal:
* Eu amo muito a Sarah. (I love Sarah very much.) This is the most literal and straightforward translation.
* Eu a amo muito. (I love her very much.) This is a more poetic way of saying it, using the object pronoun "a" instead of repeating Sarah's name.
Informal:
* Eu te amo muito, Sarah. (I love you very much, Sarah.) This is the most common and affectionate way to say it to someone you know well.
* Amo muito você, Sarah. (I love you very much, Sarah.) This is another common and affectionate option.
* Eu amo a Sarah demais! (I love Sarah too much!) This expresses a very strong feeling of love.
Romantic:
* Eu amo a Sarah com toda a minha alma. (I love Sarah with all my soul.) This is a very passionate and romantic way to say it.
* A Sarah é o meu amor. (Sarah is my love.) This is a simple but powerful way to express your love.
Choosing the right phrase depends on the context and your relationship with Sarah.