If there is anything better for a baby than to be cared for by one loving mother it might be to be cared for by two loving mother-figures. Think of how common the pattern was just a couple of generations back for an infant to be raised in an extended family with both a mother and a grandmother. However, if the two disagree on matters concerning the baby, it can be a potentially damaging situation.
The first thing I want to say about your mother’s habit of repeating the baby’s sounds is that it is not only not harmful but is actually very good for the baby. I’m not so sure about her repetition of the wails and cries, as that is somewhat unusual. But repetition by an adult of babbling sounds made by an infant is very rewarding to babies and is associated with an increase in baby’s vocalizations.
What you might do is compliment your mother for doing that but suggest that it might not be such a good idea to repeat the wails and cries. Tell her that the baby will interpret her attention – that is, the repetition – as approval. And that is not what you want with respect to crying. I’m guessing that she is probably trying to mock the baby’s crying sounds and facial expressions to show her how awful she sounds and looks. Her behavior probably does not have that effect but instead discourages the baby’s communication attempts. And that is exactly what a baby is trying to do when she cries—communicate some need to her parents.
Also I would remind your mother that it is not possible to “spoil” a very young baby. One of the main jobs for a new mother is to learn to anticipate and interpret her baby’s signals—distinguishing between a hungry cry, an “I’m wet” cry or an “I hurt” cry. The only way we can learn to make those distinctions is by being very responsive and sensitive to our baby’s efforts to communicate with us. Good luck to you in getting this message across to your mother without alienating her or hurting her feelings.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.