I chat her on whatsapp sembra naturale?

You use the with to say you are doing it together. Otherwise you are doing it by yourself.

Grammatically, "chat" is an intransitive verb. Verbs can be transitive, intransitive, or both. Transitive verbs can have a subject (thing doing the action) and object (thing being acted on). Intransitive verbs only have a subject - "I" in the sentence - so you need "with" (a preposition) to show relation to "her". In contrast, a transitive verb like "eat" would not need a preposition: "I eat apples." "I" is the subject, "eat" is a transitive verb, and "apples" is the object. Hope this helps! Don't worry if it doesn't make sense right away: your ear will gradually get used to how the different verbs work.

For past tense, use "chatted with" and for the present tense, "chatting with"

I talk to her on whatsapp.