Attachment issues

Some details changed for anonymity. Any advice welcome. I am trained with adults, not children and am at a loss.

6 year old.

Only child. Solo, working parent. No second parent.

No birth complications. Met all mile stones.

Is reportedly doing well in school, meeting expectations. Doesn't report any bullying and is objectively well liked by peers.

Around grandparents every day but struggles with the grandparents mood swings and 'grumpy' behaviour. House is loud.

Noted recent spikes of anxiety accompanied by feelings of worthlessness, negative self-talk and fear of just about everything over last month. Terrified of the dark and will not sleep on own. Has to be with parent.

Will lash out if asked simple tasks, physically and verbally. Quick to anger, quicker to become tearful.

Knows how to use basic mindfulness and will remove self from situations where childish adults are causing a problem, but only after attempting to stand up to them, thus igniting further discord with said childish adults.

Recently has disclosed that they do not want to be away from their parent for any length of time, that even at school they are scared because their parent isn't there. Desperately wanting to move which is impossible at this stage.

Primary parent has dx of anxiety and depression. Other parent unknown.

How can this child be supported?

The environment is very much less than ideal but is unable to be changed at this time.

Thanks for taking the time to read!