If you are going to keep Gouramis, your Mom needs to know that they are aggressive fish and to be careful and get all the other fish she wants and have them established in the tank before she gets the Gourami. *They are very territorial and if they feel they are going into someone else's home they MIGHT behave. *But if the Gourami is the first one in the tank and she decides to add other fish later, the Gourami will see them as intruders into his home and probably kill them.
I would say the minimum tank for one Gourami is 10 gallons as the more crowded an aggressive fish feels, the worse their temperment gets. *If she wants to have any other fish in the tank and have a quiet Gourami she should plan on at least 15 gallons.
Neons and Cories would be good companions, but both are schooling fish and need to be kept in groups, *[neons need at least 6 and cories at least 3] * DO NOT under any circumstances consider adding a Betta to a Gourami tank. *They are related and one or the other will die a horrible death. *
A really pretty tank would be the Gourami, 6 Neons or Tetras of some type, and 3 Corydoras catfish of some variety. *If you wanted a second Gourami just be very sure that it is NOT a male [you CANNOT have 2 male gouramis of any type in the same tank] and then you would need to go to a *20 gallon tank with the above fish.
I agree with Isabella completely.* Do not even think of getting any fish and putting into a tank until you have read the article about the Nitrogen Cycle and have your tank set up and cycled completely.* Fish are expensive but they are also living beings.* It is the kind and humane thing to do to make sure the home is completely ready for them and will not make them sick.* There are quick ways to cycle but they are expensive and then there are ways that are not too long that are not too expensive but what ever you do fix them a home that you can be sure will protect them not kill them.
http://www.fishlore.com/NitrogenCycle.htm - I have used Option 3 in the Fishless Cycle with great success and recommend it highly
Rose