Your mother should execute gift deed in your favour 

it should be duly stamped and registered 

your sister consent is not required 

Even though you funded for the purchase of the property and you had invested for constructing the house as well, since the property was purchased on the name of your mother, it becomes her own and elf acquired property.

However you can convince your mother to transfer the same by executing a registered settlement deed in your favor, she do not require no objection or any kind consent from your siblings including your father. 

if your mother is alive she can make a gift deed in your favour and thus she can take an exit from the property and you can deal with it in any manner you deem fit 

Since the land was purchased in the name of your mother in 2012, your mother is the legal owner of the property, irrespective of the fact that the consideration came entirely from your earnings. In the eyes of law, title flows from the registered sale deed, not from the source of funds. Therefore, at present, the property legally belongs to your mother.

If your mother is alive and willing to transfer the property to you, no No Objection Certificate or consent from your sister is required. Your sister has no independent or vested right in the property during your mother’s lifetime. Children acquire rights in a parent’s self-acquired property only after the parent’s death, unless the parent chooses to transfer it earlier.

The correct and legally recognised way to change the property into your name is through one of the following registered instruments:

1. Gift Deed
   Your mother can execute a registered gift deed in your favour. This is the most common and clean method. Stamp duty on gifts to a son is concessional in most States. Once registered, ownership immediately transfers to you.
2. Release / Relinquishment Deed
   If the property is treated as your mother’s self-acquired property and she wishes to relinquish her rights in your favour, a registered release deed can also be executed. This is generally used when there are multiple co-owners, but it is accepted in some States even otherwise.
3. Sale Deed
   Your mother may also sell the property to you through a registered sale deed, but this attracts full stamp duty and registration charges and is usually not preferred within family transfers.

With respect to the Benami Transactions (Prohibition) Act, purchasing property in the name of a mother out of the son’s known sources of income falls within a recognised exception and is not treated as a benami transaction, provided the relationship and source of funds are genuine and provable. However, this exception does not automatically transfer ownership to you; a registered conveyance is still mandatory.

After execution and registration of the deed, you must apply for mutation of records in your name with the local revenue/municipal authority.

In summary, you do not need your sister’s consent or NOC. The property can be transferred to you only through a registered deed executed by your mother, and once that is done, you will become the absolute owner in law.

Since it's your mother's self acquired property and is alive, there's no need to obtain NOC from your father and sister.

Do I need to get any No Objection signature from my sister?

No, you do not require a No Objection Certificate (NOC) from your sister for transferring the property from your mother's name to your name, because this is self-acquired property, not ancestral property. The property was purchased in 2012 solely with your funds, making it your mother's self-acquired absolute property, not a Hindu Undivided Family (HUF) asset . Under the Hindu Succession Act, your mother, as the absolute owner, has full rights to transfer or gift this property to you without seeking consent from any other family members. Since your sister has no legal right or claim over your mother's self-acquired property during your mother's lifetime, her signature is not legally required for this transfer .

What is the current law for document name change?

The current law requires executing either a registered gift deed or a sale deed to transfer the property from your mother's name to yours. Since you originally provided the funds, you must be cautious about the Benami Transactions (Prohibition) Act, 1988, which prohibits holding property for another person's benefit . However, your case falls under the exception where property held in a spouse's or child's name from known sources is permissible . The transfer requires proper stamp duty payment based on the property's current market value, registration under the Registration Act, 1908, and mutation with local authorities. A lawyer should draft the deed to ensure compliance with all legal requirements and to clearly establish the transfer's validity .

Yes it’s important to get noc from her as she is a legal heir if she denies then you need to file a suit and prove that it’s purchased solely from your income source 

As the property is registered in your mother's name, she can gift it to you by means of a gift deed (duly drafted by a competent lawyer), executed by her and registered. There is no need to get your sister's consent.