The idea that an A- or B+ in a college course is some sort of “failure” only applies to those needing very high GPAs for some goal (e.g. pre-med, pre-top-14-law, or a hyper-competitive major’s secondary admission process). UCB L&S CS admits all who get a 3.3 college GPA in the prerequisites (of which CS 61A is one), so an A- or B+ will not prevent her from entering the major, if that is the concern. Note that a B+ or higher still puts her in the upper half of the typical grade distribution in that course.
Unfortunately, the popularity of majoring in CS does mean that he will face more competition for direct admission CS majors, or make note of secondary admission processes (which can be very competitive at some schools like CMU, UIUC, UCSD, Washington, or Purdue) where there is no direct admission to CS or where he does not get direct admission to CS. Unless, of course, the computing industry crashes between now and when he applies to college (the 2001-2003 crash greatly reduced the popularity of majoring in CS for several years afterward).