1) take the plea for last 3 years wife never bothered to meet the child 

2) she has suicidal tendencies and has made number of threats to commit suicide 

3) that she is not fit to be given child custody 

She hs every right to apply for custody of the child which does not necessarily mean that the court is going to grant such relief easily.

So file your reply in that case, give all the evidences of her mental condition.

If the court finds that the welfare of the child is not suitable if custody is given to the mother, then the court is unlikely to pass an order in that direction. 

You collect the evidence for her mental ill health condition and express before court about her continuous mental unstable condition even before marriage which continues till this date and convince the court that the child's welfare and future will be ruined if she is given custody of  the child.

You can inform court about her disinterest even to see the child in the last for over three years or so this  negligence and her suicidal tendency will affect the child also very badly hence to reject her application.

You need to demonstrate the same before court it will decide the same 

Dear Client,

A person may file for divorce or judicial separation under Section 13 of the Act if they are "incurably of unsound mind" or suffer from a "mental disorder of such a kind and to such an extent that the petitioner cannot reasonably be expected to live with the respondent," either continuously or sporadically.

The Guardians and Wards Act 1890 gives the family court the authority to decide child custody matters, however these decisions frequently clash with individual state legislation. Thus, in order to preserve equilibrium, the court consistently prioritizes the child's best interests and welfare over the parent's. This suggests that the child should live with the parent who can secure his financial interests, a solid education, and a good upbringing. Since the mother is typically regarded as the kid's natural guardian, she frequently receives custody, particularly when the child is younger. However, the father or any appropriate guardian may receive custody if the mother is determined to be unfit or incapable of giving the child the care and protection that the child needs.

Custody is based on the welfare of the child and several factors goes in deciding the custody. You have to demonstrate that the child can be grown in a healthy environment if entrusted to your custody.

- As per Section 13(1)(iii) of the Hindu Marriage Act , if one of the parties, i.e., either husband or wife, is of unsound mind, then it is a valid ground for divorce. The unsoundness may be continuous or intermittent and incurable to the extent that it is not possible for the petitioner to continue married life with the respondent

- Hence, if she is suffering from mental disorders then it can be a ground of divorce legally 

- Further, under Hindu law, A mother usually gets custody of the minor child, under the age of five and fathers get custody of older boys, but it is not a strict rule and is primarily decided based on the child’s interests.

- Further, to win sole physical and legal custody, you should show, the court that awarding you custody is in the best interests of your child due to factors such as your existing relationship with the child, stability of the home life you provide, inability of the mother  to meet the child's needs; mother's lack of involvement due to her mental conditions. 

If you allege that your wife has a mental disorder, the burden is on you to prove your case based on acceptable medical evidence to the satisfaction of the court. If you fail to do so, you cannot prevent her from claiming custody of your 4 year old daughter. The court may grant her full custody as she is a girl child and is only 4 years old now, in line with legal provisions and relevant court decisions. 

Dear Quersit

if you have any documents related to her medical conditions than file the same before the court with your reply and try to prove the same before the court during Trial. the court may pass an order in your favour if you proved before the court that you are the best person for the welfare of the child because welfare of the child is paramount consideration for the court.

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