@Onestepup
Say something like 'My favourite styles are minimalist so our tastes aren't the same, but I can really appreciate the work you've put in and it's great you're so pleased with it'. Presumably she wouldn't be particularly keen on your choices either, but why should that be a problem? It is nothing personal to have different tastes or opinions to a friend, and she shouldn't take it that way. Don't 'just lie' to your friend.
Jesus, don't say this^^.
So many good options on here, which aren't out and out lies, but will actually not make her cry! She sounds as if she might cry.
I don't like people who lie for no reason or to get away with nasty stuff, but I equally dislike people who prize brutal honesty over good manners and kindness. "I tell it straight me" usually is just code for "I'm extremely rude, unnecessarily critical and unpleasant to be around" 🤷♀️.
As I said on page 1, it isn't lying to appraise it from her perspective and say how nice it is for her. Who cares that "I have more minimalist taste than you". Not about you is it? So this comes across as weird and unnecessary tbh.
Many options on here but;
"Ah well done! (Because she has completed a big job. Even if you don't like it, she deserves a well done), What a transformation! I think that bathmat goes perfectly with the tiles. Omg, did you do the tiling yourself? That is really impressive (Unless it is falling off the walls etc - I mean, doing your own tiling, for example, is actually very impressive, even if your oh so important 
minimalist sensibilities, mean you don't like the end result). You really have a good eye for detail (unless she clearly doesn't)." Etc.
Nobody cares what your "personal tastes" are and how they are different to theirs, when they are asking what you think of their bathroom 
.