I have to butt in here.
I am tiny, 4'10", with a "small vagina". It stretches just fine, thank you, but it is NOT the width of a penis that is an issue for me! I learned a long time ago that with sufficient foreplay I can accommodate an amazing degree of... uhhh, well, "spread". Any woman can.
But my "vaginal vault" (not my favorite anatomical term) is proportionably a bit shallow. I have had very "long" men penetrate me without problem, so long as the "hard slamming fuck" is avoided. If he hits my cervix, it HURTS! This impact can even cause spotting, the cervix is prone to a type of easy bruising and bleeding from what you would think would be a minor "bump"
I have learned to be VERY careful with toys, especially lengthy double ended dildos, as they can be very painful if I or my partner get carried away with thrusting.
The cervix is very mobile, actually responding to sexual excitement, including a "dipping motion" during orgasm so that the os, the opening in the cervix, is dipped into the vaginal pool, (the lake of sperm and vaginal secretions that forms in the vagina during intercourse) to facilitate impregnation. When doing a vaginal exam noting the mobility of the cervix is part of the exam.
If the two of you were still together I would suggest she have a full GYN exam to make sure she is not suffering from another problem, such as a partially intact hymen, or a bifurcated cervix or similar abnormality that limits her ability to receive a large penis.
Also if she has certain infections, like PID, vaginitis, or a chronic cervical inflammation from infection or even dysplasia, or she has endometriosis, fibroids, or an ovarian cyst, even an abdominal adhesion (if she has ever had any abdominal surgeries).
The bottom line is that if she hurts during intercourse, she needs to be exmained. I have NEVER found a penis I couldn't accommodate, no matter how long he was, so long as there was some control during fucking.
If you are a a fan of the "hard angry, slamming fuck" then this is more likely YOUR issue, and I don't mean the size of your penis.
(drops her Nurse's Uniform in relief)
WW