Well it all depends. Temperature on its own doesn't necessarily mean
much. If something is small and has a low heat capacity, then it
doesn't take much energy to raise its temperature. It also depends
upon how quickly it is able to lose the heat energy that it is
absorbing. It will also vary, depending upon where you put the
temperature probe, the ambient temperature and how well it makes
contact with the heat source.

There can be a significant amount of energy running through a relay,
one way or another, and although I have no idea about specific
operating temperatures, 57 degrees doesn't sound too alarming to me.
It is well below the temperature I would expect things to melt, scorch
or catch fire. The fact that you say it is 'warm' rather than 'hot'
sounds reassuring.

I guess if a relay was about to fail it could get hot (though it
sounds as though you've thought of this), or possibly if the pump was
drawing significantly more current than it should. But I think the
pump would fail quite quickly after this.

Is the car running OK? Any other symptoms?

Measure the current the pump is drawing, you can do this by pulling the
relay and poking the probes of a dmm set to read DC amps into the correct
relay socket holes, pump should turn on and the current will be displayed.
IPD listed the current draw of a new pump, if it's more than 12-15A the pump
is likely failing.