I wouldn't suggest she tries to actually enter the pyramids (unless she is especially fit and agile) as it is not easy underfoot, and a fair hike - a fair percentage of it requiring stooping quite severely. Not at all recommended for anyone the slightest bit claustrophobic either (insufficient room to even squeeze 2 abreast and roof height of about five foot in places) However, so long as she is up for spending 9 hours
plus on a coach for the return trip, there is no reason why she shouldn't go to the pyramids.
Personally, from Hurghada, I would prefer to visit Luxor (tombs, , Karnack etc) as there is far more to see and do, not so far to travel (3-4 hours by road each way) , and a far nicer city than Cairo but I can understand why someone would want to see such a wonderful site.
Also please be aware that both Cairo and Luxor are exceedingly hot in the summer (May-Oct) with temperatures into the forties. As Cairo can get a bit polluted, it can feel almost "smoggy" so she should be prepared for this - Hurghada in comparison will seem cool in the mid thirties!!