Hola Ricky,

The word "modelo" as model is invariable, as you guessed, so it will be modelo for a man and a woman, however we do need to use the appropriate article when it is needed:

"La modelo llevaba un vestido azul largo" (it refers to a girl/woman)

"El modelo llevaba una chaqueta vaquera" (it refers to a guy/man)

Saludos

Inma

Hola Tonya

Sorry about the delay. We didn't receive notification of your message. Just saw it now.

Yes, as the imperfect tense is also used to express a repeated action in the past, you could also translate it as "she used to be a model". However if you want  to emphasise the fact that she was and now she isn't we'd probably use verb "soler" for that, saying:

"Ella solía ser modelo"

Saludos

Inma