Brought home new Maine Coon today - Very concerned about weight. Advice?

Hi there. First time poster here.
We bought a red Maine Coon female who we've called Jessica from a local breeder and picked her up today. My wife went to get her and brought her home and whilst shes extremely fun, super friendly and curious and not at all scared on her first day in a new home, I'm really very concerned about her weight.

Shes 15 weeks old and we just weighed her and shes only 1.1kg. She literally feels like a skeleton. Stroking her is unpleasant as you can feel every part of her spine.

We've never owned a Maine Coon before and The breeder told my wife that she thought Jessica has had a growth spurt but her body weight 'hadnt caught up' - Also she felt that maybe she wasnt too great at competing with her siblings for food and now that she's got her own home she should start putting on weight.

Really not sure what to think. As I said we've never owned a MC but that weight seems awful low to me and I'm wondering if we maybe have a sickly cat. We're planning on taking her to the Vet tomorrow.

Any advice greatly appreciated.

How's the kitty doing? Was the vet able to help?