Being that she s not going to be there very long that might be fine.
Tiling very uneven walls.
There is also a spot near the window trim where the wall appears to be built up too much enough so that the tile could end up proud of the trim which i m pretty sure won t look so hot.
If you don t think you can trowel a coat of mortar to get it even withing about 1 4 the tiles will further even it out when set i would investigate a possibility of mounting a cement board onto the bricks instead.
If you re tiling over an uneven section of wall the corners of the tiles may stick out slightly from the rest of the tiles.
One very big problem that not many people realise if the wall isn t really flat a brick joint pattern will show off every out of plane point in the wall by virtue of sticking out a half tile from the tiles above and below it.
The problem is that the wall is uneven.
Preparing an uneven wall surface plastering.
The board will create a perfect backing that will make setting tiles on thinset look like a walk in a park.
Back buttering is a trick used for tiles of uneven thickness like ungauged slate or handmade tiles extremely large tiles or for tiles being installed on an uneven surface.
Plastering a wall can be a super straight forward task but if you have no prior plastering experience it may be worthwhile getting a professional in to help achieving a perfectly flat surface for tiling is essential and this isn t always easy on your first attempt.
This is known as lippage and it can diminish the most professional of.