What with high unemployment a teenager with no experience can't find a job? You don't say!
As others have said, volunteering is an excellent way to get experience, and possibly a lead to a paid job when the economy picks up.
Basically this. But, a few ideas/ comments.
1. Grocery store. I know ours are hiring, and I know a friend's 17 yo son just started working at one. But he quit 4 months in, because COVID turned all the customers crazy. I worked at a grocery store in a small town, let me tell you it was HARD to get that job. You had to know someone. I got the job because my mom worked at the bank with the grocery store manager's wife.
Does she know anyone? Do you know anyone?
2. Probably not a lot of summer camps going on. I'd recommend advertising babysitting on local FB groups.
3. COVID related jobs. Does she have a car? Can she run errands and do shopping for the elderly? There are several people here in town who are doing that, at $25 a trip.
4. Restaurants, smoothie places camp counselor.
5. Cleaning services, depending on where you live.
I'm old, but my part time jobs in HS and college were:
grocery store bagger, temp employee at the gas company (digging ditches, cleaning bathrooms, loading pipe), painting dorms, making pizza, cashier at pizza place.
I'd also recommend volunteering. My niece and nephew both volunteered starting in HS at a camp that taught disabled kids how to ride bicycles. Did it for years. Now they work at Applebees when they aren't at college. Actually, niece just graduated.