I'm probably going to be of little or no help here, but the idle issue is probably being misconstrued. It's not the intake valve that would cause this and it sounds like what is being referred to is the Idle Air Control valve. This is a common problem with many cars.
Since it's been cleaned and replaced once, there has to be another issue involved; wiring connector or PCM fault involving the IAC OR it may not be related to the IAC at all. If an EGR valve goes stupid for some reason and hangs open the engine will not idle or will idle roughly.
To at least start with a clean slate, take the car by AutoZone, Checkers, etc. and have them scan it for codes. They will do this free and it only takes a couple of minutes.
Some car makers claim that a quart of oil per 1000 miles is normal but I don't like that statement at all.
No leaks means it's burning the oil either past the rings, the valve seals, or both. There is no test for valve seal and a leakdown test MAY reveal a ring problem. Nothing is etched in stone with this test.
Question. She bought it new. Does this mean 4 or 5 miles brand new or a 100 miles give or take new? The latter could point to a dealer demo that saw a rough break-in period.