Chi-Chi has a huge head start over Bulma since she already is quite a capable Martial Artist.
She won the prelims and entered the actual tournament and this was a time when the tournament had some seriously strong competitors. She defeated lord slugs soldiers in the Slug movie.
The guides put her power level at 130. That makes her as strong or stronger than the Goku who trained under Roshi.
She was also Gotens trainer and was the one who forced him to become a Super Saiyan.
Goku is an expert trainer since he created the Mastered Super Saiyan concept and trained Gohan pretty well. He has trained from so many different masters and can use all that knowledge to train her.
I’m not saying Vegeta wouldn’t do a good job since he trained trunks pretty well himself and trained under great masters but the fact that Chi-Chi is already so much stronger than Bulma and that she has Goku on top of that training her just makes me think Bulma doesn’t stand a chance.
