Soccer is a bit of a challenge because you are using different energy systems throughout the game. but a basal reduction is helpful, with BG testing and carb or insulin corrections used when possible.
Definitely do a BG check at halftime, and at any sub opportunity.
What type of pump does she use? If the pump is tubed and she removes it for games, reconnect at halftime to do the correction.
And XC practice would probably be a reduced basal for most days. On occasional days of speed intervals, you might see a BG spike.
But for a 5k race, I would not reduce basal. The trick is to have flat stable BG, and then right before the race take a small bolus.
I see about a 100 point increase for 5k races, so I always take a small bolus right before the gun.
It takes guts to bolus before a 5k race, because you may not see BG spikes a lot at practice. But races are different! Most anything run at lactate pace will cause a spike. (Your body breaks down glucose for energy (a process called glycolysis). One of the byproducts of this process is lactate. At an easy pace, your body recycles this lactic acid back into energy. At easy paces, the production and clearance of lactate can remain relatively constant. But as the pace increases and there is demand for more energy, the production of lactic acid will slowly increase. At some point, the amount of lactic acid will go beyond what your body will be able to convert back into energy. That is the lactate pace, and you will see BG spikes at that pace! A 5k race is generally run at a high enough pace that you will see the accumulation of lactate.)
Now, if she is running a race at a slower pace and not pushing into the lactate pace, she may not see the spike. But if she is putting a high amount of energy into the race, and giving it her all for 5k, then you would see it. If she crosses the finish line with absolutely nothing left, I would expect to see the spike.
If her coach is doing any time trials before a meet, you can see it there. Just try to be flat beforehand, and be amazed at the spike you see when you have finished.