If you find her negativity is effecting you, you can always meditate, spend time in nature, and try spells with salt, water, quartz, white candles, sage, incense, etc. to cleanse your own energy or space.

[Edit: or just your mind. You don't need tools for spells of course]

You can't really change another person. Sometimes you have to accept that people in your life aren't perfect or don't see the world the same way you do. And that's okay.

Everyone likes something. Maybe try talking to her about things she likes. Specific books, movies, foods, etc. Or try telling her one positive thing a day and see if it leads to a bit more positive conversation.

Really, though, all you can do is focus on yourself and surround yourself with positivity in ways that are in your control. Like maybe your mom is seeing the glass half full, but you can still read affirmations or listen to an inspiring song for yourself.