Just to remind you that even when you "do not come" inside of her, there is still some fluid that escapes when you are erect and having penetrative sex.
My advice to you is to act on the side of caution and not leave it to chance.
Absolutely a very HIGH chance.
And like ScalpMassager asks you: "Are you feeling lucky or unlucky?"
Up to you and your girlfriend if you want to wait and worry whether her period will come on time. And you will both be panicking even more when her menstrual cycle does not come on the day she has worked out that it should.
Your girlfriend still has time to get the morning after pill, but don't leave it too late - it needs to be taken within 72 hours of having unprotected sex.
I think the decision rests on: are you feeling lucky or unlucky?
(Why would the two of you chance it and she not get the morning after pill??)
based on what i said (ejaculated outside of her, 30 mins went by, her understanding of her fertile days) do you think I am very likely to have gotten her pregnant?
I suggest she gets the morning after pill just to make sure that she does not get pregnant. You can purchase these from the pharmacy without a prescription - you may need to ask the pharmacist. If not, she can get them from the family planning clinic and the doctor can also prescribe them.
Not worth worrying to find out if her next period will come on time to see if she is or isn't pregnant. Don't do this habitually though.
This medication needs to be taken within 72 hours of having unprotected sex to work.
She may know her fertility days, but there are no guarantees if she will have conceived or not.
Always use a condom - use the latex free ones if you or your girlfriend have any allergies to the latex ones.