As per the cliché, after getting hit by a truck, our protagonist finds herself in a 'swords and sorcery' fantasy world. Also as per the cliché, she is granted an overpowered ability to make her new life easier. In this case, she gains the ability to summon/create anything she can imagine as long as she has a reasonable (layman's) grasp on how the thing works. Unfortunately, the world is on the verge of being overrun by the vile, undead minions of a group of necromancers. Having witnessed for herself exactly what kind of atrocities the necromancers are committing against the living (with suffering and death being powerful fuel for their foul magic) she vows to remove the taint of their existence from the world. Fortunately, she has played plenty of shooters and RTS games to have some idea of the weapons she can use against them. However, those are designed to work against living, human targets.
The world is a fairly generic medieval fantasy world. The enemy skeletons are limited in armor and weapons to medieval level. I'm thinking of equipping the skeletons with sword and/or longbow and wearing up to full plate armor.
The protagonist has access to modern day knowledge of weapons and tactics. This includes weapons and tools that could semi-realistically be built with modern technology even if in practice the expense/complexity would be unfeasible. For example, remotely/AI controlled tanks and machine guns, and maybe even a version of the 'rods of god'. (If I find a way to justify summoning something not just in orbital position but having orbital velocity as well.)
Skeletons are animated dead. They are not so much dead bodies given life again as they are a conveniently arranged collection of bones whose parts are enchanted with magic to make them move again. Even if a skeleton is damaged, any separated parts will continue to move and act on their own. For example, a disembodied arm will use its hand to crawl along the floor and grab at opponents' legs. As long as any part is still able to move it will continue to try to harm the living in any way possible. A 'complete' skeleton will fight with any weapons it can find while any 'spare parts' will bite, scratch, grab and kick as able.
This, unfortunately, means that it is not enough to simply remove the head or destroy the brain. Also, unfortunately, the undead remains animated even if the necromancer that raised them is killed. The sheer malice of the magic giving them life ensures they only stop when fully destroyed or rendered immobile.
They are not mindless; their intelligence is at the level of an average human.
Without going into the exact mechanics, there are some general limits to the protagonist's ability. Apart from having an idea of the summoned object there is also a summoning cost in terms of energy user (think 'MP'). There is only so much MP that she can generate in a given time, limitting the size, complexity and/or number of objects summoned. Essentially, anything can be prepared given enough time, but on-the-fly summoning is limited to very simple, small items.
What sort of modern weapons could the protagonist use against skeletons, if the goal is to destroy them as completely as possible? How would you destroy large groups in the open? What about enemies occupying a town when you want to keep the buildings and any innocents in one piece? What about clearing them out of a building without demolishing it?
Note that the skeleton enemies will be actively fighting back and they will number in the dozens to hundreds. Being in melee range of them is generally a bad idea, so unless the melee weapon is particularly effective a ranged approach is probably preferred, though ammunition is a potential concern. Note that the engagement is one against many, not army vs army.
Below are my own initial ideas.
Bludgeoning weapons seem the most effective option, though I wonder how much physical strength would be necessary to break enough bones to take out an undead. The use of a powered exoskeleton (i.e. power armor) could mitigate some of the danger, but engaging in melee still seems like a bad idea.
Pistols and rifles of sufficient power will break bones - if they hit and don't simply pass through the gaps in the skeleton or glance off a bone. After the torso or spine is destroyed, hitting individual limbs would be a lot harder too. Either a form of saturation fire or expert reflexes and accuracy would be needed.
If my understanding of explosives is correct, it's the pressure of the shockwave that kills the target through internal trauma. That means that at the very least, performance against skeletons is (much?) worse than against living humans.
Useful against massed concentrations of undead. Basically, drop a mass of rocks on the enemy from as high as possible. Either artillery or aircraft drop something like the Lazy Dog bomb on the enemy. Though, like bullets, a lot of them would need to be dropped to ensure complete destruction of the target.
Throwing an acid or similar onto a skeleton might be easier than filling its entire space with bullets. Chlorine trifluoride comes to mind, which reacts violently with pretty much with anything, though this would probably not be safe for the user.
Edit: I should have indicated this from the start (but mistakenly opted to try for a general answer), but I'm most interested in the situation where the protagonist is forced into a situation of needing to dispatch enemies that have occupied the building she is in. (Because I'm finding it really hard to come up with good solutions for it.) However, I appreciate answers on all scales.