This is true for PCs, but not for Macs. It is unlikely that your daughter will run apps that reveal the differences between Intel processors.
I'm not sure that is a good statement about it being true for PC's becoming obsolete.
I used to teach CAD/CAM back when the difference between the latest and fastest and last years fastest was substantial (1988). Each new version of the software brought the previous year's PC hardware to a crawl! By 2002, the advances in hardware had eclipsed the requirements of CAD/CAM software. And you no longer had to have an "uber" machine just to keep up.
Hardware has simply continued to get exponentially faster and software requirements have by and large been left behind. There probably are some exceptions, but other than games, I don't know what they are.
For myself, my last laptop was a 2-3 year old off-lease PC. I no longer spec processing hardware and look instead for a high quality backlit keyboard, a trackpoint (I have a tremor and for me the trackpoint is more precise than a pad and has no concern of accidentally moving the mouse as I press the button), and a good display. I easily pay less than half of what they cost new 2-3 years ago and for my purposes, they are as fast as I could ask for (after I add RAM and swap to SDD). So, for me, it is really all about the quality of the user interface components! Since no fly-by-night companies can make Apple computers and Apple positions itself as a premium quality company they only come with quality interface components. Unfortunately, I will probably never own an Apple myself, because of no trackpoint.
In any case, the 7-8 year old Lenovo (using one of the earlier i5's) cost $450 when I bought it, spent another $250 on RAM and SSD and it is still very fast and capable. She uses it for word processing and the occasional spreadsheet. As a business major, I suspect it would do anything she will ever need. The frame is cracked around the display from where she stepped on it about 5 years ago. I am surprised that never developed into a serious failure!
But my point is that I do not believe any computers (Mac or PC) are now subject to becoming functionally obsolete in a few years as they used to. I believe the durability (and the look/touch/feel) of the hardware is now the deciding factor on how long a laptop is a viable (desirable). Nonetheless, I believe that newer models will likely add desirable features/improvements to extend that life.