I would advise her to be really gentle with her skin, so that she does not overdry her cheeks, and does not lead to more oil on the t zone.
For cleansing, i'd recommend a cream or gel cleanser, or oil cleansing.
for moisturizer, she should look for a specific one for combination skins, that moisturizer should bring the balance back to her skin.
That said, it's hard to find the right moisturizer, either it's not enough for the cheeks, or it's too much for the t zone. So she could also try one moisturizer for oily skins, and one for dry skins for her cheeks. I know it's not an ideal solution, but it has helped me in the past.
As for the moisturizers, those i can recommend are Weleda's almond hydrating cream, La Roche Posay Effaclar, Lavera faces calendula moisturizer (if that brand is available in the U.S.), Laneige waterbank cream 2 (expensive option).
She can also try shea butter on her cheeks.
For the makeup part, i'd say liquid or mineral (powder), it's what i use and both work well. But i'd advise her to get an anti shine product to apply on her nose and forehead, and to use at least a setting powder, setting spray for extra security. Blotting papers are also useful, they're really cheap and take very little space in a purse.