My mother has become incapacitated and we need to handel her affairs
and any legal matters for her,there was no power of attorney done but
my sister has conducted all of her affairs in the past how do we make the legal trustee?
You can file a guardianship proceeding. In the proceeding, you can request that you or your sister be appointed as guardian -or- the court will appoint a third party as guardian.
If she is not mentally incapacitated, have her sign a POA. If she is, you will need to petition
the court for a guardian.
If she has become incapacitated and there is no Power of Attorney, your only choice is to file for guardianship which requires a court proceeding.