Seeing a single mother in Equestria, especially in a smaller town like Ponyville, isn't all that rare. After all, there are nearly ten mares to every stallion, so it's bound to happen to keep the population level. That being said, a single drunk mother is a good deal less common. However, Berry Punch (with a little help from her sister) is a perfectly fine mother. It just begs the question... where's Pinchy's dad?