My mother wants to sell her home to me, but my sister has power of attorney and states she will not let it happen. What can my mother do?

Just chiming in my agreement with the others that buying her house at below value will come back to bite all of you in your behinds. Do not do it. You will possibly create a caregiving nightmare if you do and she needs Medicaid (which many people often do) and the penalty period can be years. Ultimately your mom will be the one paying the biggest price.

Even if she does not revoke POA, POA does not allow one to overrule the person they are POA for.

I have POA for my mom and she is loaning money to one of my brothers all the time. My other brother and I do not like it, but she can do what she wants, evne if I have POA

"My mother wants to sell me her home for 20k the home is worth about 90k"

You never know when Medicaid maybe needed. Mom could fall and break her hip and end up needing care in a NH. There will be a Medicaid penalty. The penalty doesn't mean someone will need to pay for her care, but it does mean you or sister may have to care for her during the penalty period.

So yes the house needs to sell at Market Value. The only thing I see here is once Mom passes, that you buy ur sister out.

You can't actually expect your sister to give up her inheritance so you can get a gonga deal on the house while she is the full time caregiver for mom.

If you want to buy the house you need to pay fair market value and not take advantage of your mom. At 95 she has challenges physically and mentally, it is just how it is.

You should give up trying to get the house at 20k, it could be construed as financial exploitation of a vulnerable senior.

If I were sis I would be willing to sell the house to you at market value. Selling it for less will cause sis as POA problems with trying to get mom qualified for Medicaid if she needs it. The difference between the market value and 20k you propose paying is 70K and also the amount of the penalty Medicaid would charge mom with. That 70 k would have to be paid out of somebody's pocket for long term care for mom.

If your mother sells the home for below market value and later needs Medicaid there will be serious problems. This may be why sister is opposed to sale.

Ditto.
As long as your mother hasn’t been certified as incompetent in a court of law and/or has a official diagnosis of moderate to severe dementia from a qualified doctor -
she does not need your sisters permission to do a dam thing!

These power crazy POAs and DPOAs who think they have authority “over” the person really chap my hide.

I agree with PP that your mom can likely revoke the POA, but you need to be very careful if your mom might need Medicaid in the future  Selling a property to a related party can be scrutinized, as to was it sold for fair market value and if it were sold for less, there could be a gift imputed.

Your profile merely addresses age related decline, which doesn't necessarily mean there's any cognitive dysfunction involved.  So, assuming Mom is capable of making her own decisions, and as Worried states, she can revoke the POA.  

If it's a springing POA and the conditions don't exist for it to "spring", then your sister doesn't have the authority to prevent your mother from selling to you.

Best take your mother to the attorney who drafted the document and have her/him prepare a revocation and notify your sister.  

Has your sister made efforts to take over finances?

If your mother is of sound mind, she can revoke the POA and tell your sister to go pound sound. A POA is something you have FOR someone not something you have OVER them. POA doesn’t give your sister the right to override your mother’s decision or control her.