Normally, I would say to sell as you still have enough value in the car to pay off the debt and buy another car. Problem is that if you sell for $9k and payoff $5400, you're left with $3600... Being a youngish guy who is very mechanically inclined, I have absolutely zero issues finding a car for that price or cheaper that can be reliable or made to be reliable.... However, as a single mid-50's female with no mechanical abilities, I don't see this happening... (unless you have some friends/family who can help with tools, etc...)
The Buick is reliable, has low miles and is useful for when you use it... If you were my mother, I'd tell you to pay it off and keep it... Ride the bike when you can and just make sure you keep the Buick maintained with fresh oil and basic care...