I have lost track of how many times I have heard this.

Problem:
The gender of the noun does not match the gender of the pronoun.

Explanation:
The noun “bimbo” comes from Italian and refers in Italian to a male child, male infant, or male baby.

As Dictionary.com explains, one of the definitions of “bimbo” in American English is “an attractive but stupid young woman, esp. one with loose morals.”

I do not know how a masculine Italian noun became a feminine English noun that is disparaging and offensive but makes no comment on the target’s sexuality.

But, ever since I learned enough Italian to appreciate the gender pattern in masculine and feminine Italian nouns, whether singular or plural, I have been bothered by how ignorant “She is a bimbo.” sounds.

The feminine form of “bimbo” is “bimba”, which gives us the solution.

Solution:
“She is a bimba.”