#Help me find a #television #WhiteWhale please!

I think it was an episode of #UnsolvedMysteries or #AmericasMostWanted from the early years?

It was about an arsonist & the actress who played her apparently did SUCH a good job that a bunch of people reported her the tip-line.

Vague memory: I can see a picture in my head of an older lady holding a lit match, with a super creepy look on her face.

Please #Boost so I can use my brain for more useful things than worrying about this. Thank you.