Should I use "her" or "she"?

Solution 1:

"But" functions as both a conjunction and a preposition. If you look at "but" as a conjunction, it leads to that other sentence -- "she does not like you".

But if you look at "but" as a preposition, it means "except for". https://www.merriam-webster.com/dictionary/but If "except for" were substituted for "but", the preposition would take an object, in the accusative case. One of the examples given for this use by the Merriam-Webster dictionary at the link I cited is "no one there but me", where "me" is the proper case for a prepositional object.

For the sentence cited in the question, the equivalent correct pronoun would be "her".

Since so many native English speakers would use "her" in this instance, it's probable that this is the way they hear the sentence, and just naturally treat the word "but" as a preposition. This makes "her" not just commonly used, but also arguably correct.