Sounds like she had this issue before the sink replacement because she asked the plumber while he was there, and she wouldn’t be using the dishwasher when everything was disconnected while replacing the sink.
Check the filter, sounds like you haven’t cleaned it out before.
Maybe something plastic fell on the heater core and melted.
Check the vent filter on the pipes underneath your sink, replace it if you haven’t replaced it for a few years.
1-1/2 in. or 2 in. PVC Mini Vent Air Admittance Valve