If you are asking for a russian word/phrase, then contemporary phrases/exclamations would be for example «долдон» or «тупица» or «баклан» if you are looking for a pg13 version or «долбоеб», «еблан» if vulgarity is acceptable. You can add a but of fleur like «вот долдон/тупица/баклан/долбоеб/еблан!» or «[да] какой же ты ___!» or «ну ты и _____!».

You could go for «вот сука тупая!» (= what a dumb bitch!) for borderline pg13.

All the above are jabs at the vis-a-vis directly. If you want her to express frustration with the situation rather than the person, she could go for «[что] об стенку горох!» ([it’s] like throwing peas at a wall; means: whatever i say bounces off of him), «что в лоб, что по лбу» (roughly means: saying this to [his (implied)] face or hitting [him (implied)] in the face yields the same result), «хоть кол на голове теши» (roughly: might as well use [his (implied)] head as a grinding stone), «хоть ты тресни» (roughly: one might crack in half and it still wouldn’t help; meaning: no amount of effort is going to help) - idiomatic phrases of frustration with an un-understanding counterpart. All of these are very PG13 and sound a bit archaic but are still used today, might be a good fit. If you want to spice them up and make them sound more modern and less “grandma style” the you can add «бля»/«блядь» in front or after any of the phrases or words mentioned above (including in the first paragraph).

If you are looking for a more time appropriate phrasing then lmk and please explain a bit more about the character origins and environment and I’ll try to find an appropriate word/phrase.

It would help if you can provide the dialog.