She found a collection of valuable art that was being held in trust and was being stored for future sales. She wanted to be the agent to sell the paintings and didn't know how much to ask for in salary. Similarly, Liz without an art collection to market was just another Girl Friday. Both parties could win here. First, we determined her value in the matter.
Paintings increase in value as the artist becomes better known.
If Liz got the paintings into the hands of collectors, her work would be the ultimate reason for the increased value whether or not she was still actively marketing the works. Therefore, she could credibly negotiate for some residual commission on all works sold after she leaves. Any salary could also be structured as a draw against commission. Since her risk is higher with a draw, her reward should be higher than on a base or salary. On the other hand, if the estate wanted to take on the risk, they could simply pay her a salary for a year or two and have no commission.