Heather is a single mom as Tom, her spouse recently died. Heather's two daughters are ages $5$ and $7.$ Her spouse died without a Will and the estate settlement was complicated. She does not want that for her children so she decided to see a notary to draw up a Will. Heather has decided to appoint her sister as a $\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_$ for her daughters to ensure they are cared for should she pass away while they are minors