@EdinTiler she can't do that, bring in another tiler to correct work with out first giving you the opportunity to rectify and work, this she should do in writing and only when you have refused or failed to do the work can she bring someone in, where did she buy the grout etc and can you get copy invoices from the shop to prove she purchased them, do you have any photos?
Can you get a statement for any other trades that have had issues with her similar to your predicament.
If it was my job I'd be starting legals tomorrow morning without hesitation.
If she has had the work carried out again request her to provide copy invoices of everything from the smallest item to the labour to install, don't leave any stone unturned mate.
I hate people like this who think they are better than the tradesman that works his fingers to the bone to provide a nice job and a good service.
Clean her out, if that don't work wipe her out......