15 Gallon Freshwater stocking

I don't think any plecos can survive in a 15 gallon tank...she should try otos instead.

Sorry, no plecos. Try otos like lilim.

otos will need an established tank, not just cycled. also a steady supply of algae or veggies as a replacement. not good fish for beginners.

you mention that she wants plants. in a properly balanced planted tank algae shouldn't be an issue. my guess is that she will get some low maintenance plants anyways which wont need a lot of light or supplemental nutrients therefore eliminating the two main causes of algae. now its not always that simple but there are simpler ways to get rid of algae than buying fish not suited to the tank

a UGF is enough biofiltration for the tank, but a small HOB would be good for some mech filtration.

as for stocking, keep it simple. I say 3-4 of platies or guppies (all male) and maybe a betta. snails could also work well.

im gonna assume the tank is heated so

5 neons, 5 pygmy cories, 2-3 male guppies or platys (no females! the last thing that tank needs is fry...)

good setup id say and for plants try java moss and java ferns. good hardy plants that need not a lot of light and care.

I like the idea of a pair of honey gouramis with some male guppies. Try aponogetons, anubias, java fern, java moss, wisteria, and cryptocoryne for plants

How about one albino bristlenose pleco. The albinos generally don't grow longer than 3". I have two in my small tanks, one in each although I do plan to upgrade to a larger tank in a few years. They do need hiding places, driftwood, fresh veggie slices, and algae wafers; they won't live on just algae alone.

Java moss is a great low-light plant; you can wrap it to to a log or driftwood with fishing line.

I'd be cautious about filling up the tank with fish while it is cycling. If you want to do a fish cycle, try something hardy like 4-5 Zebra danios. They are also good for eating fry if you choose to get a few guppies or platies.