Sorry that is happening. Unless the filter has a setting that adjusts the flow, we don't want to block the flow too much or we shorten the life of the motor.
I like the panty hose idea a lot, but fry can get stuck to the panty hose mesh. Also debris can get tangled there.
Sonni is right that a sponge filter is best with fry. They also are a nice back up (later) if your regular filter stops running. However there are also some work-arounds...
One would be to check with your local aquarium shop (probably where you bought the filter) and
see if they sell an extension tube for the filter intake. If they don't have that, Google "aquarium power filter extension tube" and see if there is a match for your brand & model.
Probably they will not have intake holes in them. If you can find one like that, buy it. What the extra holes do is they spread out the sucking force of the intake, hopefully allowing fry to escape.
If the extension tube has no holes, put it into a vice or have a friend or family member (those are not exclusive) put on heavy leather work gloves. Set a piece of scrap board on a flat surface. (We use plywood over the air conditioning cooler, weather permitting.) Put a small bit into a power drill and drill lots of tiny holes up & down the extension. Hopefully that will make the water safer for fry.
Another thing you could do is buy a portion of the inexpensive, fast growing, floating hornwort. The outflow of the filter will push it away from the filter. Fry tend to swim towards light & the surface and they may shelter in or near the hornwort. That stuff (with or or 2.5 watts of light per gallon & at least 8 hours a day) also sucks a fair amount of ammonia out of the water.
If you wish to save future batches of guppy fry and raise them up to full size, you may wish to consider getting another 10-gallon tank. Place the gravid female in there about 1 to 2 weeks after dropping. Cover the new gravel with gravel from the old tank, put filter floss or that sponge filter from the old tank in there to help import the nitrogen cycle. Put as many real or plastic plants in there as you can. Even those bright, soap-less pot scrubbers can be unraveled as "plants." (Later use them to remove green algae from tank sides.)
If she is well fed with a little live food or frozen stuff (defrosted in Luke-warm water in a soap-less jar, rinsed gently under a slow faucet in a fine-meshed net to get rid of the "organic soup" they sometimes come in) she will be satisfied enough that she should leave her fry alone.
Even some other livebearer species much more famous for their cannibalism (Gambusia, red tailed
Goodieds, Brachyraphis species) can be graaaaadually fed little bit at a time until they can't take any more food. Be careful that there isn't uneaten food in the tank - take it out with a siphon or turkey baster/ pipit dedicated to all things fishy. At that point they leave their fry alone because they have no room for them. ;)
Hope your fry grow up outside the filter. :)