This is pretty laughable. I think it should be a reminder of the risk of excessive government intervention into things the involved politicians don't understand. Personally I think there are some reasonable arguments on limiting magazine size (not that I advocate for it), but it's clear she has no idea what she's talking about.
Magazine limit laws serve zero purpose. None what so ever in terms of actually doing anything good to either reduce crime or the impact of a potential crime.
There are already WAY too many magazines out there right now above any arbitrary imposed limit law. There is zero way to get these out of circulation. They are not disposable goods and they do not go bad unless mistreated.
It is far to easy to MAKE any magazine for any firearm out there. In fact, it is easy enough for anyone to make from scratch their own gun, ammo, and magazines for the gun. So long as people have freedom to purchase the tools of manufacturing as well as the materials to make guns they are not going to disappear in America. Not from any criminal intent on having a firearm.
But suppose an arbitrary limit law on magazine capacities does make the next mass shooter think that they don't want to break that little law before they commit a whole bunch of murders. That the next mass shooter is going to think to his or her self, "My area has a limit of 10 rounds capacity for my magazines for my illegally obtained firearms, I guess I should go get some legal size magazines before I go ahead with my killing spree after lunch."
Assuming that scenario, which is ludicrous, there are plenty of other ways for said killer to "get around" an artificially imposed limit law. They could, carry more guns! They can learn how to reload the gun without fumbling. You know they might actually try to practice how to do it quickly.
There really is zero actual good an arbitrary capacity limit law will do. The ONLY thing it will do is limit a law abiding citizen, you know those people that are trying to follow the law and not go on killing sprees, and that person's ability to defend themselves in a scenario where they may need more than 10 rounds and didn't have time to grab extra magazines to reload from.