Offering to be a surrogate

My sister has been trying to have babies for 7 years

I have 3 healthy babies

Would it be rude to offer to carry her baby for her?

I don’t know if she wants that or not.

Updated:

My sister has PCOS, her body can ovulate if forced but none ever stick due to her uterus never getting thick enough. She’d have to do some work to be able to produce eggs, but, it’s possible. I offered and told her not to say anything now, just to always know if that’s what she wants I’d happily do that for her. I don’t know if we will ever get to that point. But, I’m happy that she knows how much I’d do for her.

Thank you for all your advice! I might just be a surrogate for another family someday too. 🤗