Depending upon how much room you have (or a place to hide it, under or behind plants, etc) you could make a 55G trash can filter. A DIY wood covering or something would also work, adding an extra 50G to the system.
It more or less is a giant filter. With lots of media to maximize BB area and multiply the water volume. Water is pumped into "can" (I used a plastic one) and then flows out when it gets to a certain height, pouring back into the pond.
Can she get a little bit bigger Pond / exchange it?
Guppies and Endlers are great! You might need to consider a hungry pond companion (to keep the baby numbers in check) or nice
LFS to take them to later when the population goes up too much.
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New to FW fish? First tank in a long time or EVER??? Need some info on keeping fish?

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