Since your father had share in the said property, after his demise, all his legal heirs, including your sister would equally inherit your father's share in the property. So the 100 cents, under the law would be divided in to 4 parts equally i.e. your sister, your mother, and you two brother. (Unless there is mutual partition deed, or WILL of your later father).
If your sister goes to the court, then she can ask for revocation of sale already made by your brother of his 45 cent, and if you do gift deed or sale (makes no difference) she can also seek revocation of the same. The court, in a given facts of the case, may or may not revoke such deed is different thing, but legally that remedy exist to her.
Additionally, whether you do gift deed or sale deed, it make no difference, because first of all you have to pay equal stamp duty on the document, and second it has to be compulsory registered, and gift is as good as conveyance, except that in conveyance consideration passes, and in gift no consideration passes. So either make no difference, as in civil law suit both are vulnerable against other vested rights.
So answer to your question is
1) It make no difference if you do gift or sale deed.
2) Since sister is not included, she can at any time file law suit and seek her share in the property for the entire 100 cent, whether sold, gifted or otherwise held.
I am practice in Gujarat High Court. Should you have any query then feel free to ask.
Vivek N Mapara