Why hire a lawyer for $1,900? If the work was done as specified on the contract, then you should be paid. In PA, a small claim is upto 3,000 dollars. File a small claim and let the contract speak for itself. If she wanted to hire a real arborist, then she should have shopped around. Certified arborist around this area butcher trees all the time. A tree will not die within a year or two.
Put the claim in small claims court, they probably won't show.