I’d have used a colour remover to get rid of the old colour completely then bleached it up to a pale yellow then toned to light ash blonde in one longer appointment. I can’t be doing with full head of bleach foils over several appointments to end up with patchy coloured, dry hair.
Definitely don’t go for a highlift tint. It won’t do much other than cause it to dry out more and ....lowlights?? You won’t get a light ash blonde with low lights, so I don’t know where they were going with that suggestion.
Sounds like you need to find an experienced colourist who does more than just offer the standard menu of full head foils/t-bar highlights.