I found that the right primer can do wonders. I have dry skin yet use matte foundations as I love the coverage and lasting ability. If I use the right primer I can use any foundation from matte to dewy and everything in between.
Sounds like she needs to prime the dry areas with a hydrating primer and a matte primer for the oily sections. However until the acne clears she’d want to be careful with primers as they can block the pores.
I’d recommend using a mineral based foundation eg, Nude by Nature, Dusty Girls (Moogoo’s makeup range) or Youngblood as they have ingredients that treat the skin as well as covering up the acne and you can top up the oily sections as the day goes on and they don’t get cakey.