Can I ask what size this tank is? What other fish are in the tank?
Unless you already have a game plan on what to do with the fry, letting them into the tank to fend for themselves in the shelter you provide us usually the best option overall. The the tank is not over populated or heavily stocked with other fish, there is a good chance of plenty of fry surviving... which will increase the tanks population. If you plan to sell or trade the fry to a lfs or a fish club, etc. once they are big enough, then 2 extra tanks should be considered, 1 for the male fry and one for the female as soon as they are sexable, usually by 3 wks of age. This will help to avoid the excessive breeding I mentioned in my earlier post until you have the opportunity to rehome them.
While the breeding net that was mentioned is preferable to the hard plastic breeding shelters, it still poses much of the same problem with lack of circulation and filtration within the breeding container. Oxygen depletion is another concern. I am not fond of the breeding containers, especially for livebearing fish, unless it is temporary to confine them until they can be moved to another tank within the same day or by next day. Long term in these breeding nets/containers is not a healthy environment for them beyond that 1 - 2 days.
While in the breeding cup/net you will need to do some water changing from tank to the breeding container to help remove excess waste (food and solid fish waste) and to replenish O2. Using an airline tubing will give you the most control for siphoning solid waste out of the breeding container while not sucking up the fry, and then adding water back to the tank, making sure it is replenished to the breeding container during the process (don't add fresh tap water directly to the breeding container, only "tank water") would be the best way to keep things healthy and stable until the fry can be moved.
After 20+ yrs of breeding livebearers of all types, I still prefer to heavily plant the tank at all levels at least on one end and allow the fry to hide and survive on their own. Their growth rate tends to be faster and their overall health tends to be better this way. As the fry grow larger then they can be moved to another tank, sold, or traded... whatever you wish to do with them. If you don't wish to be overrun with fry in a short period of time then a 2nd tank can help, allowing you to mix male/female only when you are ready for breeding to take place. (this is called controlled breeding)
Best of luck to you!