Is it normal for my girlfriend

Depending on what the birth was like it might not even be safe for her to have sex yet. Did she need stitches? Her whole downstairs will be sore and tender.

Besides, you have a baby now. Her whole world has been turned upside down. Her body has drastically changed, she is probably very sleep deprived and she is now a mummy - she has to reassess everything and get used to her new role in life.

Just be patient. It will happen. And watch out for signs of post natal depression. A baby is a huge responsibility, don't let her think she's doing this alone.

She's probably physically and emotionally exhausted. Tiny humans need a lot of care and attention. When she finally gets a minute to herself she probably wants some breathing space to relax.
Also, she's still recovering from the act of giving birth. Sex after childbirth can be uncomfortable/painful (I'm told). Hormones could still be all over the place. She could feel less attractive than before. She could have some postnatal depression. She could subconsciously fear getting pregnant again. She could just be exhausted.

Maybe maybe maybe. You'll never know unless you talk to her but yeah it's normal.

Baby didn't come out of her mouth did it?

Just give her some time and treat her with love and care. Be a good husband.

Yes, that’s not uncommon at all. Good chance she’ll get back to her old self if you give her some time.