Please help me do the right thing with this teenage girl. Moms and teenage girls you input PLEASE.?

WHEN WHERE WHY Asked: Please help me do the right thing with this teenage girl. Moms and teenage girls you input PLEASE.?

I am a 25 year old single guy that works in an office.A coworker Ann is a 35 year old single mom.She was having a hard time with a project she was working on so I volunteered to help her. It often involved working late in the evening. We would work until about six and then go to someplace nearby to eat. Often her 15 year old daughter Amy would join us for the meal. I became good friends of both Ann and Amy.Amy was having trouble in school with math and Ann knew I had a college degree in math and she wanted to know if I would help Amy.

I agreed. About 3 times each week Amy would email me with her math problems and I would email her back how to solve them. This worked out for Amy as she raised her grade to an A.Both Ann and Amy were very grateful for my help.I guess I became a father figure to Amy as she would at times send me email asking questions about her starting to date boys.I gave here the best advice I could and she appreciated it.

I got an email from her today that asked What is the best method of birth control I can use?

I dont think I should be talking to ANY 15 year old about birth control.I considered

1. Ignore the email.
2. Forwarding it to her mother.
3. Telling her the facts about birth control.
4. Telling her to talk to her mother BEFORE she became sexually active.
5. Telling her 15 year old girls SHOULD NOT BE HAVING SEX.

PLEASE HELP ME DO THE RIGHT THING HERE.

Is there another better option I have not thought of?

Mothers if this was your daughter, what would you want me to do?