Without context, there’s no way to know. Either way might work, but assuming that it was correct in the first place to phrase the question as “is this Maria?”, the answer would be “yes, it is”. In English, as in other Germanic languages as well as French (and, I believe Slavic languages), we use the neuter pronoun until a person has been identified. Once you’ve identified her by saying “yes, it is”, you would then use the feminine pronoun, “allow me to introduce you to her”. Here’s a context in American English that might surprise you: Paul calls Maria on the phone: Maria: Hello? Paul: Hi, is this Maria? Maria: Yes, it is. (Typical) Yeah, it’s me. (Also typical, a bit less formal) Yes, it is I. (Technically “correct”, but rarely used) Note: In British English, the question would be “is that Maria”, but I believe the responses would follow the same pattern.

If the question is: "Is this Maria?" The response would be: "Yes, it is." Or, "yes, this is her." "Yes, that is me." But it would not be: "yes, she is." Whereas, if the question is: "Is Maria there?" Then, assuming someone other than Maria responds, the answer would be: "yes, she is."

Depending on the context both are correct. It can refer to things and also refer to a subject. In conversation it can be used like this: You ring Maria a woman answers and you ask "Is this Maria? and she answers "Yes it is!" Maria is the subject so it is okay to say. 'Yes it is.' I'd be interested in a grammarian's point of view. This is the way I answer a call when the caller asks if I am Bill. So be aware of how some English speakers use it.

Yes, this is she.

'Yes, she is' or 'Yes, this is her' 'It' is used for inanimate objects (table, plant, chair) or animals (dog, cat)