"her colleague and she/her" which pronoun should I use here?

I read a friend of mine writing this and I wondered if that was incorrect.

her colleague and her were working on the web app

shouldn't this have been:

her colleague and she were working on the web app

?

Since the person working is treated as a subject, the subject case should be used. This becomes more evident if we consider that, would we use the alternative order for the complex subject, "Her and and her colleague…" wouldn't sound correct at all. It seems that the grammar here should not depend on such a trivial matter as word order. Is only correct "Her colleague and she were working on the web app.", in my opinion.