My daughter wants to start a business, I don't know how to help her.

She will need business plan too

She would have to be properly qualified and insured and have some idea about accountancy, parts, advertising etc.

No-one will or can employ her until she has completed an appropriate training course of 3-4 years and passed the necessary qualifications.
The best way to help her is to support her, either financially or with encouragement, depending on both your circumstances.

www.gov.uk/set-up-self-employed

Are you in the UK? If so there is loads of info on gov.uk about starting a business. If she intends to do electrical work she must get properly qualified and will need liability insurance have a look at citizens advice web site too.

Usually there is a local group to support those starting up their own business, but qualifications are essential for electricians.

Libraries in the US offer seminars about how to open your own business.

What is her experience with customers and external repairs (not done in your home)?

This may help, she needs qualifications.
www.simplybusiness.co.uk/knowledge/articles/2018/07/how-to-become-a-self-employed-electrician-uk/#:~:text=In%20order%20to%20work%20as,EAL%20or%20City%20and%20Guilds.

Tell her to get properly trained.
It takes about 4 years I think but understand there are differet routes.
Suggest she talks to her local college.