She is spending her own money and her rich friend's money to give her team a good salary and a chill work environment. I don't see a problem with that.
Workout tracking is a fun project. It's relatively simple in scope and you can customize it for an audience of 1 -- I did something similar to brush up on RN development:
There is a difference between "table-stakes" complexity and premature complexity. I'd argue that a simple but sane CI / deployment pipeline takes relatively little work to set up and falls under "table-stakes" in that even a pre-pmf team will have a positive ROI in doing it.
On the flip side I have been the one working long nights and weekends reverse engineering code by engineers who prematurely built complexity into the system because they wanted to add a GraphQL api in addition to a rest API. All while in the pre-pmf days, with no value-add to the features that ultimately DID find pmf.
I do generally believe that cleaning-up after the pmf-hunting phase is itself a privilege that many startups do not get to experience, and should be treated as such. I understood the author as arguing that we shouldn't chase shiny things and should ruthlessly avoid complexity in favor of finding pmf. This philosophy is clearly illustrated in the devtools startup he is running. I thought there were some cool ideas there.