I think it would be a major red flag. Everything else in your application would have to be stellar to offset a faculty member saying she doesn't think you're ready. Having said that, I strongly advise paying attention to what your professors are telling you; it is probably for a good reason. Going to grad school because you aren't sure what to do next year, or because you're afraid of the unknown aren't good enough reasons. You have to be sure about your research interests, what you want out of a grad program, and that you're ready for the rigors of grad school, otherwise you risk burning out. This is especially true if you go right out of undergrad. Your professor is right that most undergrads are not ready for grad school right after graduating- this is because many undergrads aren't yet sure about their goals and interests and, as a result, end up struggling. I'm sure you're intelligent and perfectly capable of performing well in grad school, but if the people who know you academically are telling you to take a break, you should consider why they are telling you this. I, and your professors I'm sure, don't write/say this to dissuade you from ever going to grad school, but it sounds like you still have to figure out your ultimate aims and research questions before embarking on such a long and difficult path. Sorry if my response sounds harsh, but grad school is something you have to be really sure about, and at the moment you sound a bit ambivalent. Either way, good luck. I hope everything works out well for you, whichever route you take.