If MIL gifts her house to us - do we need to pay stamp duty?

[deepest]

just wondered....

Not if there is no mortgage left on it, according to the HMRC website:
"If the property is received as a gift there's no SDLT to pay, so long as there's no outstanding mortgage on it. But if the person who receives the gift takes over some or all of an existing mortgage, then SDLT may be payable if the value of the mortgage is over the SDLT threshold."

(SDLT = stamp duty land tax)

No but you could be liable for other tax as you can only gift up to a certain amount in any one tax year.

The tax liability may also depend on how long MIL lives after the gift, and also whether the gift is considered to be deliberate deprivation (?) of assets to avoid tax (or care home fees) which can lead to complications (and being taxed/charged as if the gift had never occurred).

It's worth getting proper legal/financial advice on this.