if she's on meds, i suggest she uses a high SPF sunscreen. then reach for good brands, Clarins, Vichy, La Roche Posay... the kind you tend to get in a pharmacy, not a supermarket because those clearly aren't the best.
the one i use and am certain is non comedogenic is one from La Roche Posay called "Anthelios fluide extrême". it won't grease your face unless you put a lot on, it's milky so you really don't need much product and it won't clog your pores. it's also absorbed quite easily by the skin. they have SPF 20, 40 and 50 versions.
they also have a stick for your lips, quite good but it makes them white lol.
anyway, i hate sunscreens on my face and it's the only one i can use. i also know that brand provides a great UVA&UVB sunscreen (they claim to protect against the whole range of UV rays).
by the way you mention Mexoryl, this one contains it too

(well, LRP is owned by l'oréal).