If you can get one, a breeding net or box will do the trick. They go inside the tank and keep the babies safe. Boxes often have a slot of some kind that the babies can get through, but Mom won't fit through. Nets simply hold them, and keep other fish out 'til they are large enough to fend for themselves. Often have to be assembled, but it's not hard to do that. Hang over the tank front or side.
You can try to put Mom in the net, but sometimes it is stressful for them to be moved. If not, you have to try to catch the babies and pop them in when they are born. If you are not around when that happens, Mom may eat quite a few of them. Same for the box, but if you can put her in a breeder box, most of the babies will probably survive at first.
If you don't have a lot of floating plants with nice long roots, java moss can provide hiding places inside the tank for fry. I think they even make plastic stuff that will provide hiding places for fry. It is instinct for them to hide if they can find places to hide in, which helps them survive if they are born when you are not home.
Baby fry need tiny food. You can get fry food, or crush flakes to a fine, fine powder, if you get caught by surprise. Hard cooked egg yolk, rubbed to mush, is good fry food too. But don't use much, it will foul the water if not all eaten. Tiny, tiny amounts, and if they eat it all, then you can give a bit more. Fry should be fed at least four or five times a day at first, as they cannot eat much and have small tummies.
I feed microworms to fry, in a breeder box. They live for several days in water, so I can feed once a day and they pick them off the bottom of the box as they need to. Don't know if you can get microworms, but it sure saves me feeding so often. These are Endler fry, a bit smaller than molly fry, but not much.