It's really hard to evaluate without knowing all the information. There must be much more that we don't know.
I had severe PND, and was admitted to a mother and baby unit, so I could stay with my baby, but receive constant supervision and support. There was a wait for this though, and in the meantime baby and I went to stay with my parents, as my husband was fantastic and did all he could to support, but after a month he had to return to work to pay our bills. Mental health services visited me daily through this period. There was never any mention of social services, and health professionals could see baby was well cared for by my mum and dad, with me doing bits as much as able.
I work as a paediatric health professional and work with several babies whose mums are in Foster care placements with their babies, again, for constant supervision for safety but to enable mum and baby to stay together, or live with their parents like I did, again for supervision. The baby is sometimes placed under the responsibility of the grandparents but the mum is encouraged to do as much caring as she can, with supervision
I wonder if she was offered either of these, and how much her family supported her. The first choice of social services is nearly always to place baby with an extended family member. The second choice is a mum and baby Foster placement with a professional Foster carer. 3rd, or in cases where severe MH concerns its a mum and baby unit. We don't know if any of these were offered, and if not, why not. And why was baby not placed with Dad?
It's incredibly sad, but to just blame Social services is likely to be an over simplification of a very complex issue