Somebody was having trouble fighting with only one pet

In that case, they should try to advance through the storyline(Assuming they're still a new player), rather than immediately play in the Fest Zone, since battling in the Fest Zone will be significantly easier if they have the second, and eventually third, pet slots unlocked.

They can buy a second slot in Esior's Haven at the Sylesti Plaza.

Once they reach Umbra Forest, they can buy their third pet slot in the Sanctuary of Saerielle at the Plaza.

One thing that'll also likely help them is having gear that matches the level(At or not too much below) and stats of their pet. Epic rarity gear and above is usually the best route to go, but if they're a lower level, it's very much understandable that they may not have access to either the gear or gold yet to buy better gear.
So, assuming they're still new, they should just look through the gear they currently own and equip what best matches their pet's stats.

Water - Strength and Agility

Air - Strength and Dexterity

Shadow - Intelligence and Agility

Earth - Agility and Strength

Fire - Intelligence and Dexterity

Light - Intelligence and Agility

If they need gold, they should send their pets on Missions, since Missions will give them gold, and an amount of satchels, depending on how well they were performed.
This is a mission guide that may be helpful:
https://www.sylestia.com/forums/?thread=12841

And these are some other threads/guides that suggest ways to make gold that may also prove helpful:
https://www.sylestia.com/forums/?thread=2280
https://www.sylestia.com/forums/?thread=93706