Legal Question in Wills and Trusts in California

There's not enough information to give you a definite answer. If the person was competent to change her will (i.e. knew what she was doing), then she could do so. However, if she had been unduly influenced (not just "encouraged") because she could not resist due to her medications and/or physical/mental condition, then it could be challenged when the time comes. You might try to collect as much documentary evidence of her inability to resist as you can in the meantime.