Coloring hair

I know people are probably going to freak out over a box color for hair but just hear me out! My sister is a cosmetologist and bleached my hair in February or march and said she would do it again to fix my roots. It's incredibly nice of her to do it for me but we aren't very close and I don't want to keep asking for her to redo it. And honestly even if she said yes she wouldn't do it for at least a few months. Normally I would go pay to have it done but these next two months we are tight on money and I really just need a boost since my hair looks like crap. Could I use a box color to color my hair brunette since it's been a few months now?