Oh wow...I have a swordtail....this whole time I thought it was a platy! D:
Anywho~ it is pregnant!
and in the late stages. Looks like you have perhaps a weak left!
I'm pretty sure they're livebearers. You need to separate her from the other fish eventually of the fry will die from being attacked, eaten, or sucked into the filter. I'd suggest getting a separate tank (a 5 gallon would do). If you do not have the necessary funds, then a net breeder or divider will work just as well.
To know when to separate her: male swordtails may begin to nip around her anal fin, her belly starts to look square, she may become territorial, she separates from the others-often near plants or gravel (this is about the last sign that they're about to give birth)
If you choose to get the net breeder, then your goal is to wait until the last signs of pregnancy (try to keep her in their for under 24 hours). This is just a guess but I'd say the belly becomes square like near the last week. Males will nip near the anal fin around the last week. She'll become territorial during the last week and a half (varies on tank size), separates from the group usually a day or hours before birth.
If you're wondering what to feed the babies just feed them crushed flakes. I have no clue on the growth rate of swordtails, but I'd guess it takes two weeks+ before you start to see some serious growth. You can't add them to the tank until they're big enough to not get eaten-even then you may want to wait an extra week just to make sure.
If she is still pregnant after birth FEED her. She will eat her babies. If not then return her to the tank to allow fry to grow.
Hoped this helped!
