First of all it is to be ensured that if the principal of X who is a GPA of the said principal, is alive on this date.
Whether the GPA deed in her favor is valid on this date.
The sale agreement in her favor will not confer title to her to the property.
She should have a valid sale deed duly registered on her name to confirm marketable title to her on the property.
If X is not having any right to sell the property, any action intended to be done by her either in US or in India to transfer the property by sale is invalid.
You should be aware of the legal fact that a GPA is not the owner of the property and if a GPA is trying to sell the property on behalf of the principal, the said principal has to ratify or to submit a life certificate to effect the registration of the sale deed in favor of the prospective purchaser.
A sale agreement entered between a buyer and vendor cannot be a title document and will not confer marketing title or rights to the property under agreement to the buyer.
If both the above issues are not clarified properly there will be no use to buy this property which may fall into litigation sooner or later by which the new buyer will have no respite and may stand losing time, energy and money.
Consult and take an opinion from the local lawyer before venturing into purchase.