I have an 11X34 on my custom Guru. It works perfectly. She might have to get a different derailleur, but it's a good option when you have a compact and you need to be able to climb big hills.
I have a 28 on my other bike, which is a triple (I've gone from a 25 to a 27, then 28) and the compact has lower gearing. It took a bit for me to get used to the jumps between gears, but now I like it. I don't use the lowest gears that often, mostly when I am very tired coming up my street/driveway after a long ride. But, I know I will be using them in the Berkshires, etc.
2015 Trek Silque SSL
Specialized Oura
2011 Guru Praemio
Specialized Oura
2017 Specialized Ariel Sport