MY 4 MONTH OLD KITTEN IS IN HEAT, WOULD SHE FEEL PAIN DURING SEX WITH A NEUTERED KITTEN? QUESTIONS?

she is a part bengal kitten n soo cute. her and my other male kitten who is nearly 8 months old were in the garden. he was doing his own thing and she was doing her own thing. she sort of positioned her tail up and lay down flat and you know did the flirtyish behaviour cats do when in heat. so to make sure she was in heat, i put her next to my other kitten to see if he would respond. btw he is neutered. and next thing you know he started sort of biting his neck. you know the kind of thing the males would do. i will get her spayed and will not let her out in the garden, as i am scared she may jump over the fence and become pregnant. but if my kittens did have sex, would she pass out in pain? she is around 4 months old and obviously my male kitten hasnt developed those spike things on his area, so would it still hurt her?