Running ethernet around the house is a no go as everything is decorated and carpeted etc.
Have you made sure she’s on 2.4Ghz for improved penetration?
You have three simple choices:
1.Put the effort in. Strangely most people I know have some form of floor covering and have decorated where they live, just because it’s slightly more difficult doesn’t bescissarily mean it’s not possible, flat cables as mentioned can be used, external runs etc. to the loft space and then drop an AP into the upstairs ceiling centrally.
2. Spend money. For those unwilling to pull cable, mesh systems exist, if that’s not an option then powerline may work with an AP.
3. Put up with the nagging.
Three is a short term option at best, one is the best option but likely requires the most work, two is the least invasive and potentially just as expensive as one, but technically inferior. Choose your poison