For issues you find with the Switch and Console releases, please follow this link and give as much detail as possible. This is the speediest way to get info to Pipeworks and get a hotfix in the works.
For issues you find with the Mobile 1.3 update, please follow this link and give as much detail as possible. This is the speediest way to get info to DR Studios to look at your issue. Also, some troubleshooting hints here.
Does your friend have an item in the pet slot? If so, that means the item in the pet slot is overriding any pet that is being summoned. Remove the item from the pet slot and it should be fixed. The pet slot appears with the grappling hook slot and the minecart slot, where you would equip those as well.
Did she put the pet dragon in her pet slot? The one in her pet slot has higher priority over the one she’s using. She can right click the fish in her inventory to move it to her pet slot as a possible solution.