You didn't word it exactly like this, but basically you want to sell her
your 1/2 of the house and take her mortgage for that amount (which is
like her putting 50% down - her 1/2).

A 10 year 4% mortgage for $22,500 means a $230/month payment. Surely
she could pay that.

A mortgage with all the standard clauses gives you the right to
foreclose for failure to pay, sell the house, and have first dibs on the
proceeds.

Foreclosing is probably not a real option for you, but having a mortgage
that has that in it makes it more likely that she will pay.

You can't get blood out of a stone, as they say, so your best bet is a
mortgage that she CAN pay, regardless of the terms. E.g., a 20 year
mortgage with $120/mo payments is still better than nothing.

If she doesn't want to buy your half, you do have the right to force a
sale to get your half. Also probably something that you don't want to
do, but does give you some negotiating leverage.

Good luck - your situation is one of the more unfortunate ones that come
with "family".

Bob