hey so have started a campaign and a player has chosen shadow sorcerer and ive found some homebrew spells that reflect that shadow nature of other places and she thinks that because of that shadow nature there should be some necromatic spells and i kinda disagree any opinions 

also 

so with wizard finds learns spells and sorcerers have spells that just come from them, if so can they learn spells little help please thanks 

Not with how the rules are written, you can choose new spells with level ups but not learn additional ones outside of leveling.  Depending on the DM they may allow you to look at some of the additional spells from UA and similar sources, but that is your DMs choice whether they allow it.  My personal opinion is that shadow magic is not necromantic by nature, it interacts between the boundary of life and death but doesn't really have a whole lot of brings things back to life flavor.

I'm of the opinion shadow magic is necromantic, depending on what type of necromancy is being used. Shadow and darkness is often used as a counterpoint to energy and life. Where light is often thought of to heal, darkness is thought of to devour life. Draining. So, necromantic spells like Inflict Wounds, Enervate, etc seem very thematically appropriate. Shadow magic could be less about death and zombies but still very much be able taking life away like necrotic damage.

Darkness is also seen as the void - the negation of energy. So spells that remove energy or negate magic are also thematic: such as Silence, Counterspell, Dispel Magic, and Antimagic Field.

Darkness is themed as spacial and dimensional. While Light has a theme of speed darkness instead favours teleporting. Great abysses like Outer Space, portals, and such: so things like pocket dimensions fit the theme as do spells like Demiplane, Teleport, Misty Step, Dimension Door, Plane Shift and Gate and so on.

Darkness is also a theme of seduction, deceit, treachery, privacy, shrouds and the hidden. So spells like Charm, Dominate, Private Sanctum, Magic Aura, Modify Memory and many illusions would also fall into this theme.

In many interpretations Light and Dark covered all existence: so at the core, thematically/symbolically, half of everything could be attributed to darkness. This was actually the creation story and important plot point in the universe of Top Cow comics which brought us The Darkness and The Witchblade, and also a theme in TV Series Supernatural (God is Light, his sister is Darkness). So really, how far you want to stretch what is thematically Shadow/Darkness is really up to you.

And by you I mean: the player and the DM who should work together. But I will say, if she wants to include some spells that deal necrotic damage then yes this is very on brand for the theme of shadows and darkness - at least according to most of all creative fiction and even in our real world mythology going back to our most ancient civilisations. So, your view of darkness and shadows not being necromantic is very much unsupported by literally several thousand years worth of real world mythology and stories. But hey, your DM's world, not mine.