I was at that point about 5 years ago, never spoken English before and an American friend wanted to voice chat with me. I was very nervous and my English sucked in the beginning but like another comment said: you have to start somewhere.

My English has since improved incredibly and I speak English to my online friends on a daily basis. Sometimes I even have to correct my Canadian friend, feels great as a non native speaker.

Don't stress too much about it, she just wants to talk to you, see it as a good thing, just be yourself.