Elle est têtue comme une mule.
ell lay tay-TEW kuh mewn MEWL. Click below to hear the phrase!
She is as stubborn as a mule.
French has a whole long list of such comparisons, which are a standard part of conversation, though clichés all. Think of têtu(e) as related to headstrong. After all, head is la tête.
Note one little difference in the syntax (the way the words are strung together). In English, we need as…as to make a comparison. Though sometimes we leave out the first as, it is always understood (she is stubborn as a mule). In French, when you are using one of these “set” comparisons, you use the verb être (to be) + adjective + comme (like) + the person or thing you are comparing to. It’s like saying She is stubborn, like a mule!
Other such comparisons are riche comme Crésus (as rich as Croesus, from Greek myth–look him up) and pauvre comme Job (as poor as Job, from the Bible). Do you know other comparisons?