Edit: The yearly exemption limit is now $15,000
No tax consequences to you.
Tax consequences to your sister. From your comment:
My sister is single, but my wife and I have a son. So we can avail
$14000 x3 = $42000 without the need to report it. The remainder
($70000-$42000) = $28000 will be reported against the lifetime
exclusion by my sister on her return. Per my understanding, the $28000
is also not subject to any gift tax
It is subject to gift tax, and she must submit gift tax return (form 709) to the IRS. On that return she can choose to apply part of the lifetime exemption and reduce the lifetime limit, or pay the tax and keep the lifetime limit. If she applies the exemption, she needs to keep track of it, so that it could be properly applied next time, or when she passes away.
The lifetime exemption is in fact intended for the estate tax. But people can chose and apply it to gifts during lifetime and reduce the exemption for estate. This is something of consequence to take into account.
Yearly $14K cap is not related to the lifetime exemption and is for gifts per donor per donee. Breaking the gift into several occasions over several years helps reducing the tax burden on the donor without touching the lifetime exclusion and affecting the estate tax. But if you don't have the time...