Just my thoughts...rambling as they might be
Women become surrogates for a variety of reasons, you might ask (in a non nosey way), I'm interested in what drew you to surrogacy?
It could be "I liked being pregnant, but know another child of my own is not practical, or whatever" for some women it is the act of kindness - we often see that in a close relative or friend, for some, but not all, it is money however underlying the money someone would need another reason to do it for money, because a pregnancy takes a toll on one's body. But to make assumptions and or judgment without knowing is harmful to you (as evidenced by your posts).
Again, you might ask why CA? Not Ohio? Perhaps it is a desire to earn more money, perhaps it is a self preservation method for her and your cousin - less likely to run into them accidentally. Or any number of other reasons.
Medical records sent to a stranger or unknown entity? You may not know the extent of her research. Certainly the prospective parents need to know about any blood or body fluid exposure to their baby. Or risk of genital herpes, or preeclampsia risks or any risk to their baby.
As to travel or procedural things, I'm sure the agency explained that before contacting with her. I suspect it is the discussion on female cycles and stuff that is freaking your cousin and you. Discussion of human sexuality is often uncomfortable.
As for travel and care of the biological son during these trips, again I assume it was discussed with your cousin. Maybe you are protective of your cousin, maybe your are making assumptions that it is an inconvenience when it may not be. Maybe your cousin herself is worried about becoming attached to the other couple's baby and is projecting it in a way placing a "this is a burden because"
It seems to me that you are unable to process why she is doing this, followed by all the reasons to question the sameness of this endeavor.
But I could be way off base.