I think you need more information here. Are these timed tests something that is a regular, weekly part of the regular classroom activity? Or is the mom seeiing that the kids are having these tests but she doesn't realize that these are not part of the regular teaching but are standardized aptitude tests that are administered, once, maybe twice a year?
The tests as you describe them sound to me like a standardized aptitude test, the kind of thing that all school systems now require of students at all levels. I would be surprised at a K having those kinds of activities as just part of the regular classroom work, unless it was a K program for academically advanced kids. Ask the mom if these really are regular things or if she is mistaking required aptitude testing for something it's not.
If the mom has issues with it she really needs to sit down with the teacher and get into what the girls are doing on these tests and why the teacher wants them to repeat K. It sounds as if the mom feels the teacher wants to hold them back because the girls didn't do well with these tough tests--??. The key thing is-- what is expected of them in first grade at this school? If the girls are expected to have mastered these operations before going to first grade, and they have not, then yes, there IS a reason to have them repeat K, very possibly; the mom needs to find out what lies ahead, not just focus on what she thinks her kids shouldn't be asked to do right now.
If the academics is not the reason for the recommendation to repeat, then the mom needs to find out what is really going on and if the issue is maturity. And maturity is a real and legitimate reason to hold a child back; I've seen kids who should not have gone on to first (who really should not have started K when they did) and who ended up going to first and then struggling because they were not yet ready.
No matter what, if the girls need to repeat, it is FAR easier to do that in K than to wait and possibly set them up to repeat a grade later on when doing so is socially much more difficult.
If the teacher is just pushing the kids too hard because she wants to be tough, the mom needs to find out why and what the principal and first grade teachers think about it.