No, no, no, no, no
that is not the meaning of birth control.
The meaning of birth control is using a condom, a diaphragm, going on the birth control pill, using an iud
your girlfriend can ovulate at any time during her cycle, that means there are no safe days, I repeat no safe days.
You can't just say we'll have sex only on days 1-10. I usually ovulate on day 12 or 13 and two months ago it was day nine...You never know. If I was using your method to not get pregnant, I would probably be pregnant.
This is a silly way of thinking you are practicing birth control and your girlfriend will most likely end up pregnant.