Is this possible?

If the base color of your hair is not colored then there's no need for your hairstylist to lift the color of your entire hair.  In order for her to color your hair a light brown, she'll have to either seperate the highlights to only color the dark part of your hair, or she'll dye your entire hair light brown, and then rehighlight them.  In order for you to go from light golden blonde to beige blonde highlights, she might have to use a color stripper (like Colorfix) to get the highlights lighter, and if that's not possible (if they don't get light enough), she might have to highlight them again.  If all she adds is color and strips the highlights it shouldn't be too damaging.  Now, if she highlights your hair again, then it might cause some damage to it.  Ask her if it's possible for her to separate the highlights so that she won't have to color your entire head and then rehighlight.  It might take longer (depending on how thin they are), but still, it is a LOT less damaging.  Also, she doesn't need to bleach your entire hair to achieve a light brown, a volume 20 or 30 oxidizer should be enough, if needed 40, but there's no need to bleach your entire head.  After that, make sure you deep condition once a week to maintain healthy hair, twice if need be.

Good luck and let us know how it turned out. ^^