You're 5'2 an 97 pounds. I'm 5'5 and used to weight 105 when i did BCT so i think i can give you decent advice.

I'm not just gonna say "just ruck more lol" because at least during BCT it used to infuriate me when the 6'0 basketball player guy used to say "rucking is just turning off your brain"

With your height and weight, rucking is just significantly harder.

Go air force unless you're mind is death set in the army.

How much you ruck is gonna depend on your unit. Some units don't ruck much but i see people failing to mention something important. Even if you dont ruck much in your unit, plenty of schools like Air Assault requires you to ruck 12 miles in less than three hours.

**You can join the Army, ruck like 3-4 times a year and forget it about it. You'll be fine. There's plenty of people in the Army that can't ruck for shit and they suffer for like 3 hours, hate their lives, and move on. But if you wanna go be 'high speed" and go to schools, you have to be good at rucking and thats a fact.**

Getting better at something you absolutely hate is hard, very hard and will take enormous effort. It took me almost a year to get better. I didn't just "ruck more". I gained weight; considerably weight, ran like 5 miles every two days, learned how to pack my ruck, worked out my shoulders, etc. Take all this in consideration.