I have a 2007 335i coupe, and it's been so-so on reliability. As said above, the HPFP is a 120k mile warranty, and the turbos are warrantied for 8 years/82k miles. According to my trip computer, I average 25mpg. On summer blend it's closer to 27mpg. With cruise set @70 on the freeway she'll do 32+. That's boring 4 cylinder Accord MPGs in a 300hp 6 cylinder; this car really amazes me with fuel consumption.
I've never had any fuel pump issues, but it has been updated to the latest revised pump and injectors. I HAVE had the oil filter housing gaskets leak and the water pump fail. Those two repairs can be done in a weekend by a shade tree mechanic, hell, I did it.
Near as I can tell, the water pump has more to do with the plastic impeller and housing than the turbochargers, so pretty much all the BMW inline 6'ers suffer from this issue.
I also had a pretty wicked wastegate rattle, and they would have eventually failed. My turbos were warrantied recently.
Honestly, if she's not an enthusiast, get her a 328i x-drive. Better yet, get her an X1. It's based on the E91 Wagon, and surprisingly several thousand cheaper than a similar equipped 328i.