Really need advice on how to manage a horrible situation at work.
Basically, I returned to work in mid March after having taken 10 months of maternity leave to have DC3. Just before I went on mat leave, the company was sold so that we have new owners. My boss left and I report into a new boss based in the US and have several new team members globally. Quite a few members of the team were made redundant but noone in the UK (London) where I am based.
I have been in my position for 13 years and hired the junior person (C) into her role about 3 years ago. She actually started as an intern who came in as her mother (who I know very vaguely) asked me if she could do some work experience at the company. I agreed. C was good, worked hard so I ended up hiring up (made a case with my boss) initially on a FTC which we made permanent after about a year. We worked together well for about 2 years until the company got very busy indeed. Both C and I worked long hours to tackle the ever increasing workload, not helped by us being given a huge project to deal with and no extra resource. I believe C was working hard as she was aiming for a big pay rise and bonus. I recommended to my boss and HR that she be given one but it was refused as noone of her grade were eligible for bonuses and she had been given a pay rise less than a year previously. I tried to persuade my boss to change his mind and said that it would create a flight risk if we were unable to increase C's salary but he refused. At the time the company was private equity owned and there was very little appetite for investment/retention of staff.
Once C found out she was not getting a pay rise or bonus, she became very upset (tears in the office), then stopped talking to me (grunted in response to questions, glared at me etc) and went on a "go slow", taking ages to do anything, doing the bare minimum, not meeting deadlines. I tried to give her time as I knew she was upset and tried talking to her but nothing worked. I gradually grew annoyed as it meant I had to pick up a load of her work when I was heavily pregnant so I was working long hours and massively stressed. Her attitude towards me was also pretty upsetting.
So, last June I finally go on maternity leave, having rolled out this project nearly singlehandedly. The company was sold just before I left, my old boss and lots of my team members who I'd worked with for years left or were made redundant and my maternity cover started. I came back to work in March to find C and my maternity cover (who is staying on in the company but in a different role) openly hostile to me. We had a handover meeting where my cover was blatantly rude, questioned decisions I had made, things we had done as a team and criticised me for not managing C properly. She was basically saying C has had a dreadful time, I have come along and fixed it all etc. It turned out that the new owners of the company allowed us to hire extra resource into the team so C was less busy/stressed and my mat cover (lets call her J) had way more time to supervise her. It also turns out that C has been slagging me off to J and to my new boss, saying I underpaid her, never had time for her etc. Luckily my new boss does not seem to have taken it seriously and it supportive, but C continues to be horrible to me. She glares at me when I approach her, gives me one word answers, and I often see her and J talking about me. My first day back I could see them in an office laughing and clearly bitching about me.
I have tried to give it time but it doesn't seem to help. I tried talking to C to try to clear the air. She basically listed all the reasons she hates the job (boring work, wants to do more interesting, high level things etc) and I have tried to address her concerns. I involved her in training I was doing (I prepared it all and let her deliver half of it), sent her to Paris on a work trip, try to give her interesting work, allow her to work from home etc but it's clear she hates me and is miserable in the job.
I've mentioned to my boss in passing that C does not seem overly happy but I don't want to make a massive issue of it mainly because it makes me look bad! Apparently C was delighted and really happy when J was her boss. So it is obviously personal.
Would appreciate advice on what to do. The atmosphere is so toxic I honestly feel like resigning