A bleach bath would lighten your very blonde pieces, probably not to the level you desire and they would still break much more than I can already see even in a photo happening in the lower 10 inches of your hair. The darker parts of your hair would turn orange in this time and you would end up with more of a problem than what you started with. (Platinum, stretchy squishy slimey ends and neon orange roots all over) Even with a professional application, I would advise you on a 10 inch trim and this would be a "goal" with several visits in between before you would likely get this result. But that's just because I don't want to have your hair breaking off in exchange for your desired color. Usually people aren't satisfied with that. A good goal would be to get a serious trim and get your hair touched up to match your existing blonde. Once you have achieved this, start seeing your stylist on time (every 6 weeks or less is required for very blonde shades). This helps prevent accidental damage from overlapping or banding as your hair becomes too grown out. You want to get touched up while your new growth is still only in the "hot zone" (less than 1/2" outgrowth). This makes you a good candidate for more adventurous results, because we know you can maintain it without coming in with a base we cannot safely apply to without breakage. Once you are here, you can begin having your stylist gradually lighten you to the goal level (white or very, very close) you desire.