Foundry mishap

[Mowmail]

I was in a friendly match with a friend of mine on the map foundry.
She rushed her soldier right to my base and I didn't see it coming b/c of the vision limit. She reached the corner and by then the only troop that could reach there was a scout. Since a scout only does one damage and the soldier does 2. She wiped out my base and won. Has anyone else encountered this problem? If so, how would I counter it?