It's quite funny because she used to peak for the GS tournaments. In 2017 she was barely top 100 for most of the year (even dropped out briefly) yet made R3 of Aus Open, Wimbledon, and US Open. After the US Open she was only ranked 82 despite having three GS third rounds on her ranking.
Now she is a top 10 player and her last four GS results have been R2/R3/R2/R3...
She used to always beat these types of players until about 8 months ago, now she has a lot of losses against players she would never lose to before, for example Trevisan and now Zhu.
I don't know if it is coaching that needs to be changed, I mean Tom Hill brought her from being a top 50 player to top 3. Last year her results started to not be good anymore so I was thinking maybe it's time for a change, but then she made the final of Guadalajara out of nowhere and qualified for semifinals of WTA Finals.
She has a lot of points to defend between now and Indian Wells (St Petersburg F, Doha SF, Indian Wells F) but after that not much until October, so hopefully she'll play with less pressure when her ranking drops a little bit because as we saw in the match against Zhu she was too passive and allowed Zhu to dictate play and it seemed that Maria was afraid to go for her shots and kept hitting in the middle of the court
I am proud though that Maria at least tried her best and fought until the end as she always does, in an era when there are many lazy/unmotivated players on WTA who always give up and don't care.