How old/large are the guppy fry? It isn't a myth that guppys will eat their fry and each others, but in my experience many guppys will only pay interest in guppy fry when they are very small/young, once they reach 1-2months old they are largely or completely ignored.
The question you have to ask yourself, is do you really want to raise 17 guppy fry? Remember that its only going to take 3months til they are sexually mature and well on their way to being half grown or more and ready to be rehomed, although it may seem like enough to time to work out what you are going to do with them when they are mature, time flys by with guppy fry. Do have somwhere like a lfs that you know for sure will take the fry off you once they are suitable size? If you keep some of them, you also have to make sure they cant breed with each other or any close reletave guppys.
Personally, i would just buy some nice densley leaved plants, and make a good area in the tank which is densley planted- the fry will instinctively hide in the plantd area once born, and its unlikely the mother guppy will chow down more than a few if she does decide to eat them if she's only there for a couple of days- you also have to remember that not all guppys will eat their fry, come will completely ignore them totally.
Most fry that get eaten by the mother are weak to start off with, the reason why some guppy mothers eat their own fy is actually to weed the weak ones out at the start and give the strong and healthy ones a head start in life

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17 guppy fry in a breeding net is rather crowded, they are not going to able to much growing in it, personally what i would do if you really, really want to raise these fry, is leave 7 or so of them in the main tank and just raise 10- of them in the breeding net for a 3weeks/a month to give them a head start, the chances are some of the guppy fry that go in the main tank will survive as well

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