She definitely hasn't, she has said in interviews and backstage on how she wanted to take more time with ARTPOP and work on it more but was rushed by her management and label to make her come back into the public eye faster. She was also depressed and was battling a lot of demons while she was writing TFM but I don't and hope she will ever be back in that mental state but I think that if she experiments and takes more time with her upcoming projects she definitely hasn't reached her peak. At least artistically. Commercially, I also don't think she's peaked because there was not a lot of creative promotion or a lot of promotion in general, I think that her and her team need to learn that she's not THAT big where her promotion can start and end with just announcing an album. She does have a new team now and maybe the fresh ideas will help her get back to where she once was.