I have naturally medium brown hair and recently I've been able to lighten it to a pale blonde (photos are in my timeline); and some parts are white. I need to retouch my roots but unsure how to do it w/out overlapping. I went to a salon, paid 150, and they were only able to get my roots to orange. Yeah, that was money wasted.

Since the roots are already lifted a bit, I was thinking of continuing to the blonde I have. I bought Loreal Quick Blue Bleach (used it before, love it), 30 developer, blue based toner, and lots of conditioner.

I'm absolutely terrified of overlapping because if any chemical gets on the bleached hair, I know it will disintegrate! Already when wet, my hair is as fragile and the slightest pull snaps the hair.

I was thinking of coating the already bleached hair with a deep conditioner or cholesterol and wrapping it in foil to make sure it's isolated from the bleach and retouching the roots that way.

Does anyone have any other method to protect the bleached hair?

The best way to go with this is to use a tint brush and section your hair very carefully. Don't paint the bleach on too thickly to prevent it running.
I think the cholesterol idea is definitely worth a try since it's so thick it may help protect your hair.

I have my brush and everything. Wish me luck! I'll let you guys know if I'm bald this evening.