My friend has a multiple tourist visa right now, she wants to apply for an h2b visa now. Will it affect his tourist visa. Thank you.

For first time H-2B, it's best to apply at the US consulate in your friend's home country. She may apply while in US but be careful... If her change of status was denied, she would need to leave US immediately otherwise she will become illegal, and after 6 months of illegal status in the US she will be ineligible for any visa. H-2B visas are also subject to 214b considerations, just as tourist visas are.