Intermittent cooling light issue

My daughter's Gen 2 Prius is having an oddity with the indicator lights related to the cooling system. She had her inverter water pump replaced recently (the "red triangle" warning light came on and this is what was diagnosed). Within a few hours of driving away from the garage the red triangle light came on again, and this time the main display screen indicated an issue with the cooling system. The diagnosis this time was a "slow leak" in the cooling system which would require eventually the replacement of the main water pump. The garage topped up the coolant level and off she went.

A few days later, the red triangle light came on again, and once again the main screen indicated a cooling system issue. She checked the coolant level, and it was within a quarter inch of "full," so low coolant doesn't seem to be the issue. The red triangle light came on and stayed on each time she started the car for a couple of weeks, and then this morning when she started the car, the light was not on.

Has anyone seen something like this?

A second question: When the red triangle warning light comes on in a Gen 2 prius, is it supposed to stay on until it is reset by a garage, as is the case with many "check engine" lights, or can it reset itself?

Finally, I know that the car has an issue with the Combination Meter (an intermittent failure of the dash lights). AFAIK, the red triangle warning light is not affected by the Combo meter issue, correct?

Thanks in advance for the expertise here.

 

No, she only checked the overflow reservoir.

Thanks. This is good to know.

I finally found a large detailed picture of the combination meter ECU, and the red triangle, check engine, and other "idiot" lights don't seem to be on that circuit board. Are you saying that if the combo ECU is intermittent then the appropriate idiot light may not come on? The dash only goes dark once a month or so. If the dash is on, can the idiot lights still not come on, or only when the combo ECU isn't lighting up?

Thanks much for your response!