I'm 4'11 and my daughter was 8lbs 12ozs, my son was 8lbs 9.5ozs, I couldn't have either of them naturally, I had both via c-section. My sister is the same height and had both of her babies, both under 7lbs via c-section because she was too small, it's not uncommon for a more petite women to have to have a c-section because of a narrower birth canal, the stretchiness of your vagina has nothing to do with birth, it's your birth canal that matters, and being smaller and having narrower hips, it's likely to have a smaller birth canal. BUT I have a friend who is about 5'1 and she has had 2 babies over 9lbs, one almost 10lbs, naturally, it's very possible, like kate said, our bodies do amazing things sometimes. I wouldn't stress yourself over it, but definitely educate yourself on c-sections, take a birthing class, that's what I did. I was horrified with my first that I would have to have a c-section and I took a birthing class, where they also explained what would happen during a c-section or an emergency c-section, and thank god I did because I ended up with an emergency c-section. It was so scary going from about ready to push, to being immediately wheeled away to the OR within 2-3 minutes to save my son's life because his heart rate was dropping when he tried to descend into my birth canal, and I knew exactly what was going on and what would happen thanks to that class, it wasn't as scary knowing. I just had my 2nd c-section about 3 months ago, and I've honestly LOVED both of my c-sections, they were amazing, beautiful birth experiences, and I honestly didn't have a ton of pain recovering either, within 2 weeks of both c-sections I was full recovered besides heavy lifting. I'll post you the link to my c-section experience incase you're interested in reading it. Try not to stress either way, you'll see in labor that if a c-section is the best thing for your baby, you'll be willing to do whatever, the fear will go away completely if it means the health of your baby. PLUS after being in labor for 12 hours before during my first delivery, a c-section was a blessing haha!!
Good luck hun!!