I would not sash in white. It will draw attention to any problems. If the sashing is needed for size, think darker. Maybe something that uses all the main colors. Or, just square up all the blocks, sew together and work out the size with borders. But, I think the most important thing is to let her know that almost all problems are fixable (just maybe in a weird way!) and that it is okay. This is how we all learned! She can still buy precuts, just make sure she buys from trusted sources and companies. Does she have a quilter's group in her area that she could team up with and get assistance with her cutting? Also, if she is new, her 1/4" seams might also have been a tad off - practice, practice, practice.