So I have a friend with super oily skin...

Your friend sounds like me. After a bit of trial and error over the past decade, this is what works for me:

 

OC8 8 Hour Shine Control Primer -> any sort of pore concealing/minimizing product over t-zone and areas that are prone to oiliness -> foundation -> setting spray.

I personally can't use 99% of the primers in the market because they're silicone based. My skin is oily & breakout prone. The only primer I've found which helps my makeup stay in and helps prevent oil breakthrough is Nurturing Force Blot Out Offensive. The stuff is amazing. If your friend is interested she can find it at Camera Ready Cosmetics online.

As far as foundations go, she should be using the correct moisturizer under her foundation. Brand has nothing to do with it. If her foundation is water based, then her moisturizer should be too.

The best foundations I've found that work on my skin after a lifetime if trial & error are Estée Lauder Double Wear (it really stays & covers well), Maq Pro 6 pan foundation palettes (also can be found at Camera Ready Cosmetics) and Monave Liquid Matte cream foundation (as well as their mineral foundation/concealer). None of them break me out (Monave's actually helps heal my breakouts), they last really well on oily skin & none of them feel heavy once applied. You can also get lighter to full coverage with all of them with a little bit of experimenting, depending on a person's needs at any given moment. I also love all of them because they're 'all in one products for me', meaning they work as concealers & foundations for me. The Maq Pro palette also works as a contouring product & highlighter for me. Which winds up saving me money in the long run.

Monave's products are the most economical but are incredible products, while Maq Pro is $42 for a HUGE amount of product, and Estée Lauder Double Wear about $38-$45 per 30ml/1oz depending in which country you're in.

I also highly recommend a setting spray! I use Urban Decay's De-Slick one - and i buy it at Sephora. I don't use a primer, but I use the new Neutragena shine control foundation. Using the two helps me get through a full work day (plus commuting time of course), and then I  use a facial towelette to take everything off when I get home to let my skin breathe.

 

Hope that helps! 

This is what works for my skin - oily and acne prone:

 

Wash face with cleanser - no oily stuff

 

Don't use a moisturizer or primer

 

Apply Revlon Colorstay for Oily skin foundation - has an spf so no need to apply a separate one.

 

Set with a translucent powder

 

Those that have really oily skin know that the less you do to it, the less oily is produced

For most oily skin it is best to use herbal remedy like wash face with gram flour mix with milk and turmeric and use it makes use skin oilyness ang glow your face.

Try it helps you.

I use Clinique's acne products (face wash, clarifying lotion, and moisturizer - and spot treatments when necessary) and apply Peter Thomas Roth Clini-Matte after the moisturizer has dried.  Clini-Matte isn't cheap, but I've been using the same bottle since June and it isn't even half-empty yet & lasts all day.  For treating pimples, I love Kate Somerville EradiKate.  You can only really apply it at night (unless you want to go through extensive measures to cover it up), but it definitely works for me.  If all else fails, the girls at Sephora really seem to know what they're talking about.  I wouldn't have tried any of this if I hadn't gone in there totally frustrated and desperate one day.  I also agree with the Urban Decay De-Slick suggestion.  I've only used it 2 or 3 times, but it's worked out well for me.  I hope your friend finds something that works for her!  I know it can be terribly frustrating. 

All Urban Decay setting sprays are made by Skindinavia. You're better off buying the larger bottles of Skindinavia as they're more economical. They also have several different types of setting spray to choose from, including one specifically for oily skin. Their website often has great deals. I got 3 full sized (8oz) bottles of different types of their sprays, plus a very handy travel bottle that can be refilled from the larger bottles. I believe I paid around $50 for the entire lot. One bottle was normally around $29 at the time I bought them. Great deal when you buy their package deals.

My favorites are the 10 Years Younger Spray & the Bridal Spray. But, I must say, my own custom mixed oily skin spray is better than anything I've tried from any brand.

here's what i found worked for me:

 

OC8 primer

Mattify powder from Mattify Cosmetics

tarte amazonian clay foundation

tarte smooth operator powder

Urban Decay all-nighter setting spray

 

i'd still need to use blotting tissues a few times during the day but this was the best combo i found for lasting foundation with full coverage.