My mother is selling her property in Mexico. She is planning to divide the proceeds among her 2 daughters and herself. My mother has dual citizenship. Her daughters are US citizens.

The money you receive from your mother is considered a gift, and there are no tax consequences for receiving a gift. Nor is there any tax on making (or receiving) a money transfer. So neither you nor your sister have any tax consequences here. Of course your mother may have tax consequences on the sale of the property. And if she is a US resident she may have to file a gift tax form if the gift to either child exceeds the annual gift tax exclusion of $13K. She most likely wouldn't actually owe any taxes on this, but must still file the form.

Thank you for the response. Another question, if I may, If the property is in Mexico will she still have a tax liability in the US?

If she is a US resident: yes, she reports the sale as a capital gain. However, she will be able to take a credit on her US income tax for taxes she has to pay to Mexico.